WATER    PURIFICATION 
PLANTS 

AND 

THEIR  OPERATION 


BY 

MILTON   F.  STEIN 

Assoc.  Mem.  Am.  Soc.  C.  E. 
Assistant  Engineer,  Cleveland  Filtration  Plant 


FIRST   EDITION 
FIRST  THOUSAND 


NEW  YORK 
JOHN  WILEY  &  SONS,  INC. 

LONDON:    CHAPMAN    &    HALL,    LIMITED 
1915 


/?- 


Copyright,  1915,  by 
MILTON    F.    STEIN 


;  •', 


PUBLISHERS  PRINTING  COMPANY 
207-217  West  Twenty-fifth  Street,  New  York 


PREFACE 

IN  this  book  it  has  been  the  primary  object  of  the  writer  to  give 
instructions  for  the  operation  of  water-purification  plants  as 
simply  and  concisely  as  is  consistent  with  reasonable  complete- 
ness. In  general,  it  has  been  the  endeavor  to  treat  the  subject 
with  special  regard  to  the  requirements  of  the  non-technical 
operator  of  small  plants,  but  certain  portions  have  been  treated 
more  elaborately,  experience  seeming  to  show  that  graduate 
chemists  have  some  difficulty  in  grasping  certain  phases  of  the 
work  on  first  assuming  charge  of  a  purification  plant.  This  seems 
to  be  especially  true  as  regards  the  relation  of  the  laboratory 
work  to  that  of  actual  operation,  the  tendency  being  to  neglect  the 
latter  and  lay  undue  stress  on  the  former.  For  the  benefit  of  the 
non-technical  operator  it  has  been  attempted  to  include  in  one 
book  all  information  and  data  required  in  the  operation  of  the 
plant,  such  as  instructions  for  preparing  standard  solutions,  mak- 
ing bacterial  and  chemical  tests  of  the  wrater,  handling  coagulants, 
washing  filters,  keeping  records,  etc.  For  his  further  aid,  charts 
embracing  the  computations  necessary  in  determining  the  amounts 
of  coagulants  to  be  used  have  been  added. 

To  make  the  book  more  readable  to  those  not  intimately  con- 
nected with  water-purification  plants,  a  chapter  has  been  added 
giving  detailed  descriptions  of  the  various  types  of  plants  and  their 
component  parts,  together  with  numerous  examples.  A  chapter 
on  the  natural  chemistry  of  water  has  also  been  added,  showing 
the  derivation  of  its  chemical  constituents  from  the  geological 
formations  with  which  it  comes  in  contact. 

The  writer  recognizes  that  the  treatment  of  water  is  a  very 
subtle  and  uncertain  branch  of  applied  chemistry,  in  which  every 
rule  has  numerous  exceptions,  and  begs  to  be  excused  for  the 
rather  arbitrary  handling  of  some  parts  of  the  subject  made 
necessary  to  maintain  simplicity  and  clearness  to  the  non-technical 
reader.  For  the  same  reason  the  products  of  chemical  reactions 
have  been  given  as  definite  salts  formed,  instead  of  in  the  more 
scientific  ionic  form. 

In  a  book  of  this  kind  it  is  necessary  to  draw  upon  many 

iii 


312525 


JV  PREFACE 

sources  of  information,  and  if  the  writer  has  failed  to  properly 
acknowledge  such  source  in  any  case,  the  omission  has  been  in- 
advertent. Special  acknowledgment  is  due  the  United  States 
Geological  Survey,  from  whose  reports  were  obtained  considerable 
data  for  use  in  Chapter  I,  to  The  Engineering  Record,  to  the 
Transactions  of  the  American  Society  of  Civil  Engineers,  and  to 
the  publications  of  the  American  Public  Health  Association. 


CONTENTS 

CHAPTER  I 

PAGE 

WATER  AND  ITS  IMPURITIES 1 

Common  Constituents  in  Water 1 

Suspended  Matter 3 

Acquisition  of  Chemical  Constituents 4 

Hardness '. 6 

Gases  contained  in  Water 8 

Mine  Drainage 10 

Sewage  Pollution 12 

Bacteria 13 

Typical  Streams 15 

CHAPTER  II 

TYPES  OF  PURIFICATION  PLANTS 19 

Objects  of  Water  Purification 19 

Various  Processes  Used 21 

Coagulation  and  Sedimentation          21 

Slow  Sand  Filtration 22 

Rate  of  Flow  and  Loss  of  Head 25 

Theory  of  Filtration 26 

Raking  Filters 28 

Scraping  Filters 28 

Mechanical  Filtration - 31 

Settling  Basins 33 

Coagulating  Apparatus 34 

Filter  Details 39 

Washing  Filters 46 

Water  Softening 51 

Iron  Removal 51 

Slow  Sand  Filtration  Plant  at  Washington,  D.C .51 

Torresdale  Filters  at  Philadelphia,  Pa 58 

Mechanical  Filtration  Plant  at  Minneapolis,  Minn 62 

Mechanical  Filter  Plant  at  Wilkinsburg,  Pa 71 

Filtration  and  Softening  Plant  at  Columbus,  Ohio 74 

Iron  Removal  Plant  at  Iowa  City,  Iowa       .     •• 90 

CHAPTER   III 

PHYSICAL  AND  CHEMICAL  TESTS 93 

Tests  Required 93 

v 


VI  CONTENTS 

PHYSICAL  AND  CHEMICAL  TESTS — (Continued}  PAGE 

Apparatus 94 

General  Instructions 96 

Taste  and  Odor 100 

Turbidity ' 101 

Color 103 

Alkalinity 104 

Free  Carbonic  Acid 106 

Examples  of  Tests 108 

Alkalimetry  and  Indicators 109 

Iron 113 

Free  Aluminum  or  Iron  Sulphate .115 

Excess  of  Hypochlorite  of  Lime 116 

CHAPTER  IV 

BACTERIAL  TESTS 117 

Apparatus 118 

Cleaning  Apparatus      .  122 

Preparing  Apparatus 123 

Nutrient  Gelatin 123 

Lactose  Agar 124 

Dextrose  Broth 126 

Lactose  Bile 126 

Notes  on  Preparing  Media 127 

Collecting  Samples 127 

Quantitative  Test 128 

Fermentation  of  Dextrose  Broth 130 

Fermentation  of  Lactose  Bile 131 

CHAPTER  V 

INTERPRETATION  OF  TESTS 132 

Taste  and  Odor 132 

Turbidity 133 

Color 133 

Alkalinity 134 

Acidity 136 

Free  Carbonic  Acid 136 

Iron 137 

Free  Alum 139 

Free  Ferrous  Sulphate 140 

Bacteria 140 

CHAPTER  VI 

COAGULATION  AND  STERILIZATION 142 

Description  of  the  Process 142 

Theory  of  Coagulation 143 

Aluminum  Sulphate 144 


CONTENTS  vii 

COAGULATION  AND  STERILIZATION — (Continued)  PAGE 

Lime 150 

Hydrated  Lime 152 

Soda  Ash 154 

Ferrous  Sulphate 156 

Natural  Coagulation 162 

Introduction  of  Coagulants 163 

Comparison  of  Costs 164 

Sterilization 164 

Hypochlorite  of  Lime 165 

Liquid  Chlorine 170 

Sodium  Hypochlorite 171 

Ultra-violet  Rays     .      .      .  •    .  • .      .      .174 

Copper  Sulphate 174 

Ozone 176 

Automatic  Regulation  of  Coagulants 176 

CHAPTER  VII 

WATER  SOFTENING 180 

Hardening  Constituents 181 

Reactions  of  Water  Softening 183 

Special  Tests  in  Water  Softening 184 

Total  Magnesium 184 

Incrustants 185 

Treatment 185 

Introduction  of  Coagulants 188 

CHAPTER  VIII 

SEDIMENTATION 189 

Types  of  Basins 190 

Currents 191 

Baffling 192 

Cleaning  Basins 192 

CHAPTER  IX 

FILTRATION  AND  GENERAL  OPERATION 193 

Routine  of  Operation 193 

Making  of  Tests 193 

Preparing  Coagulant  Solutions 194 

Inspection 197 

Operation  of  Filters 198 

Washing  Filters 201 

Clear  Water  Basin 204 

Laboratory 204 

Calibration  of  Apparatus .      .  204 

Organization 206 

Cost  of  Operation 208 


viii  CONTENTS 

FILTRATION  AND  GENERAL  OPERATION — (Continued)  PAGE 

Records  and  Statistics 211 

Automatic  Recorders 213 

Electric  Alarms 214 

Construction  of  Charts 214 

Economy  in  Operation 217 

General  Remarks                                                                                      .  220 


PLATE  I. — Graphical  Results  for  Tests  of  Alkalinity,  Acidity,  and  Carbonic 

Acid 221 

PLATE  II. — Graphical  Determination  of  Carbonates,  Bicarbonates,  and 

Hydroxids 223 

PLATE  III. — Amounts  of  Aluminum  Sulphate  Required  for  Various 

Turbidities .225 

PLATE  IV. — Coagulation  with  Aluminum  Sulphate  and  Lime  ....  227 
PLATE  V.— Coagulation  with  Aluminum  Sulphate  and  Soda  Ash  .  .  .  229 
PLATE  VI. — Amounts  of  Ferrous  Sulphate  Required  for  Various  Turbidities  231 
PLATE  VII. — Coagulation  with  Ferrous  Sulphate  and  Lime  ....  233 
PLATE  VIII. — Proportions  of  Iron  and  Acidity  for  Natural  Coagulation  .  235 

PLATE  IX. — Cost  of  Coagulation  by  Various  Methods 237 

PLATE  X. — Chlorid  of  Lime  Required  for  Various  Strengths  of  Solution  .  239 
PLATE  XI. — Ratio  of  Water  to  Amount  of  Chemicals  for  Various 

Strengths  of  Solution 241 


APPENDIX  A. — Analysis  of  Coagulants 243 

APPENDIX  B. — Standard  Solutions 246 

APPENDIX  C. — Specifications  for  Coagulants 251 

APPENDIX  D. — Weir  Table  .  .  253 


WATER  PURIFICATION  PLANTS 
AND  THEIR  OPERATION 

CHAPTER  I 

WATER  AND  ITS  IMPURITIES 

THE  water  obtained  from  rivers,  lakes,  wells,  and  other  sources 
of  supply  usually  contains  a  considerable  quantity  of  foreign 
matter  in  suspension  and  solution,  not  only  as  inert  mineral  sub- 
stances, but  also  in  the  form  of  living  organisms  and  waste  products 
of  organic  origin.  From  the  chemist's  standpoint,  all  of  these 
foreign  substances  may  be  considered  to  be  impurities,  but  in 
judging  a  water  with  regard  to  its  fitness  for  domestic  or  industrial 
use,  only  those  substances  which  render  it  detrimental  to  health, 
unfit  for  household  and  industrial  purposes,  or  unpleasant  to  the 
sight,  taste,  or  smell  are  so  considered.  In  fact,  a  chemically  pure 
water  is  rather  unpalatable,  and  experiment  and  observation  seem 
to  show  that  the  presence  of  certain  common  mineral  substances 
is  desirable  in  water  used  for  drinking  purposes. 

The  foreign  matter  generally  present  in  water  may  be  listed  as 
follows : 

SUBSTANCES  OF  MINERAL  ORIGIN 
In  Suspension  : 

Clay  and  Inorganic  Soil  Wash. 
In  Pseudo-Solution :  * 
Silica 
Alumina 
Iron  Oxid 
In  Solution  : 

Bicarbonates  ~  . 

n    i  Calcium 

Carbonates 


Sulphates 


of 


Magnesium 


^, ,     . ,  Sodium 

Chlonds 

XT.,  Potassium 

IN  itrates 

Bicarbonate 

Sulphates  [•    of  Iron 

Hydroxid 

Mineral  Acids 


*  Extremely  fine  particles  in  suspension. 
1 


\7ATEK   PURIFICATION    PLANTS 

f  Carbon  Dioxid 
Dissolved  Gases     i  Oxygen 
I  Nitrogen 


SUBSTANCES  OF  ORGANIC  ORIGIN 
In  Suspension  : 

Organic  Soil  Wash 

Decomposing  Organic  Wastes 
In  Pseudo-Solution  : 

Colloidal  Organic  Wastes 

Vegetable  Color 

Organic  Acids 
In  Solution  : 

Vegetable  Color 

Organic  Acids 

Soluble  Organic  Wastes 

Ammonia 

Chlorids 

Nitrites 

Nitrates 

Carbon  Dioxid 

Hydrogen 
Dissolved  Gases        Hydrogen  gulphid 

Methane 
Living  Organisms  : 

Algae,  Diatoms,  and  other  plant  forms 

Bacteria 

Minute  animal  forms 

This  list  is  neither  complete  nor  rigid  in  its  classification,  but 
presents  only  the  most  common  substances  present  in  one  of  a 
number  of  possible  groupings.  The  same  substances  may  appear 
in  several  groups,  as  often  they  may  be  of  either  organic  or  in- 
organic origin. 

To  those  engaged  or  interested  in  water  purification,  a  knowl- 
edge of  how  these  impurities  and  constituents  of  water  are  ac- 
quired, and  of  the  properties  imparted  by  them  to  the  water,  will 
be  of  interest  and  value.  It  will  assist  them  in  better  under- 
standing the  purposes  of  water  purification,  the  difficulties  and 
limitations  involved  in  interpreting  the  results  of  chemical  and 
bacterial  tests,  and  in  adjusting  the  processes  of  coagulation  and 
water-softening  to  the  varying  conditions  of  the  waters  being 
treated. 


WATER  AND   ITS   IMPURITIES  3 

Precipitation  in  the  form  of  rain,  snow,  dew,  etc.,  is  the  source 
of  all  water  supply.  Initially  this  water  is  pure,  being  the  product 
of  a  natural  process  of  distillation,  but  owing  to  the  remarkable 
solvent  powers  of  water,  it  acquires  impurities,  such  as  carbonic 
acid,  oxygen,  nitrogen,  dust,  bacteria,  etc.,  even  before  reaching 
the  ground.  After  its  fall,  it  is  disposed  of  in  three  ways.  A 
portion  is  evaporated  from  the  upper  soil  and  from  water  surfaces, 
or,  being  taken  up  by  plant  roots,  is  transpired  through  the  leaves, 
and  with  this  we  are  no  further  concerned.  Of  the  remainder, 
called  the  runoff,  two  dispositions  may  be  made.  Part  of  it  flows 
away  over  the  ground  surface  to  the  nearest  watercourse  and 
thence  to  the  streams  and  rivers,  constituting  the  flood  flows 
which  follow  heavy  precipitation  or  melting  snows.  The  re- 
mainder percolates  through  the  soil  and  only  reaches  the  streams 
after  a  more  or  less  lengthy  and  devious  journey  through  disin- 
tegrated, porous,  and  fissured  rock  and  along  impervious  strata 
thereof. 

The  rain,  by  the  impact  of  its  fall,  loosens  soil  particles  from 
the  surface,  and  carries  them  to  the  streams.  If  the  ground  is 
steep,  so  that  the  water  runs  off  with  high  velocity,  it  will  erode 
the  surface,  thus  adding  to  the  sediment  load  of  the  water- 
courses. 

The  sediment  thus  transported  to  the  streams  causes  the  turbid 
appearance,  or  turbidity,  of  their  waters.  This  is  naturally  greatest 
during  floods,  when  the  surface  runoff  to  the  streams  is  much 
greater  than  the  amount  of  ground  water  reaching  them.  Most  of 
the  turbidity  is  derived  from  plowed  fields,  from  which  it  follows 
that  in  pastured,  wooded,  or  rocky  country  the  rivers  are  com- 
paratively clear.  If  a  region,  however,  is  composed  of  steep  hills 
overlain  with  deep  subsoil,  this  may  contribute  largely  to  the 
turbidity  of  its  streams.  Rivers  also  erode  and  undercut  their 
banks,  which  is  another  contributory  source,  although  most  of  the 
sediment  so  derived  is  coarse  and  is  deposited  as  a  bar  at  first 
opportunity.  The  first  rush  of  a  flood  brings  with  it  much  coarse 
sediment,  but  as  the  flood  subsides  the  sediment  carried  becomes 
finer,  and  is  more  difficult  to  remove  in  the  process  of  purification. 
In  small  streams  the  duration  of  floods  is  short,  and  while  the 
turbidity  during  high  water  may  be  very  great,  the  average  tur- 
bidity is  low.  Many  large  rivers  are  always  turbid,  due  to  the 
almost  continuous  occurrence  of  floods  on  some  of  their  numerous 


4  WATER   PURIFICATION   PLANTS 

tributaries,  so  that  in  addition  to  great  turbidity  during  general 
floods,  they  have  a  high  average  turbidity.  The  turbidity  of  a 
water  is  measured  by  comparison  with  arbitrary  standards,  made 
by  adding  definite  amounts  of  especially  prepared  powdered  silica 
or  fuller's  earth  to  bottles  of  distilled  water,  as  explained  in 
detail  in  Chapter  III.  The  results  are  stated  in  parts  per  million. 
Thus  if  one  part  by  weight  of  the  powdered  silica  is  uniformly 
mixed  (by  shaking  in  a  bottle)  with  one  million  parts  of  perfectly 
clear  distilled  water,  the  resulting  turbidity  of  the  standard  thus 
prepared  is  said  to  be  one  part  per  million,  and  a  sample  of  water 
which  on  comparison  with  this  standard  presents  a  similar  ap- 
pearance, is  said  to  have  the  same  turbidity.  Results  obtained 
with  different  waters  are  not  strictly  comparable,  being  affected 
by  variations  in  the  color,  composition,  and  relative  fineness  of  the 
suspended  matters.  A  turbidity  of  five  parts  per  million  is  barely 
discernible;  a  turbidity  of  100  gives  a  water  a  very  cloudy  ap- 
pearance; a  water  with  a  turbidity  of  1,000  is  practically  opaque 
in  appearance.  During  floods  the  turbidity  of  a  stream  may  rise 
above  10,000  parts  per  million,  and  under  varying  conditions 
values  may  occur  from  this  down  to  zero. 

The  portion  of  the  runoff  which  percolates  through  the  soil 
absorbs  carbonic  and  traces  of  other  acids  from  the  decaying 
vegetable  matter  contained  therein,  and  from  the  excretion  of 
plant  roots.  The  acidity  thus  obtained  enhances  its  power  of 
solution,  and  enables  it  to  attack  mineral  matters  which  would 
otherwise  prove  insoluble.  During  the  passage  through  the  soil 
much  of  the  oxygen  absorbed  by  the  water  from  the  air  is  removed 
therefrom  by  the  decaying  organic  matter.  This  enables  the 
water  to  hold  in  solution  certain  salts  which  would  be  oxidized  to 
an  insoluble  condition  were  oxygen  present.  After  descending 
through  the  soil  and  subsoil,  the  water  enters  the  rock  strata  or 
glacial  drift  composing  the  upper  geological  formation  of  the 
region.  In  the  more  ancient  formations,  the  rocks  consist  of 
granite,  basalt,  gneiss,  etc.,  of  which  mixed  silicates  of  aluminum 
and  potassium,  sodium,  calcium,  or  magnesium  are  the  principal 
constituents;  the  mineral  felspar,  a  mixed  silicate  of  sodium  or 
potassium  and  aluminum,  being  very  prominent.  The  carbonic- 
acid-charged  water  leaches  the  alkalies  and  alkaline  earths  from 
these  rocks  and  removes  them  in  solution  as  bicarbonates,  thereby 
reducing  the  hard,  resistent  strata  to  soft,  clay-like  substances 


WATER   AND    ITS    IMPURITIES  5 

which  can  be  dug  with  a  spade.     The  action  of  the  carbonic  acid 
and  water  on  felspar  (KA1  Si30s)2  is  typical  of  this  process: 
(KAlSi3O8)2  +  C02  +  2H2O  =  K2C03  +  H2Al2(SiO4)2H2O  +  4  Si02 

Felspar  -f  Carbonic  Acid  =  Potassium  Carbonate  +  Kaolin  + 
Silica.  The  potassium  carbonate  and  silica  are  carried  off  by 
the  water  in  solution,  the  latter  in  colloidal  form.  The  kaolin  re- 
mains behind  as  clayey  surface  soil.  The  proportion  of  sodium 
and  potassium  silicates  to  those  of  calcium  and  magnesium  in  this 
class  of  rocks  is  such  that  the  resulting  ground  water  is  high  in 
alkaline  carbonates  and  low  in  the  bicarbonates  of  the  alkaline 
earths.*  It  results  that  such  ground  waters  are  characterized  as 
soft,  although  of  relatively  high  alkalinity.  The  presence  of  these 
alkaline  carbonates  makes  possible  the  acquisition  and  retention 
by  the  water  of  considerable  quantities  of  silica  (SiO2),  alumina 
(A12O3),  and  iron  oxid  (Fe203)  as  a  suspension  of  extremely  fine 
particles,  a  state  known  as  colloidal  solution.  In  this  colloidal 
state,  these  substances  do  not  readily  enter  into  chemical  reaction, 
and  are  difficult  to  remove  by  filtration.  While  they  cannot  be 
said  to  add  to  the  turbidity  of  a  water,  they  may  give  to  it  an 
opaque  appearance  due  to  the  reflection  of  light  by  the  particles. 

The  waters  from  a  region  underlain  by  ancient  formations  of 
igneous  rock  (or  more  recent  formations  in  volcanic  districts)  of  the 
kind  above  described  are  sometimes  called  primary  waters,  in 
reference  to  the  position  of  these  rocks  in  geologic  history.  Such 
waters  are  characterized  by  the  proportionately  (although  not 
necessarily  quantitatively)  large  concentration  of  salts  of  the 
alkalies  (sodium  and  potassium)  and  the  small  amounts  of  salts  of 
calcium  and  magnesium  present,  and  further  by  the  presence  of 
silica  and  alumina  (iron  to  a  less  extent)  in  the  colloidal  state. 

Although  it  has  been  computed  that  silicates  of  the  above 
types  constitute  98  per  cent  of  the  earth's  crust  for  the  first  10- 
mile  depth,  yet  large  areas  are  overlain  with  secondary  or  derivative 
rocks.  Often  these  take  the  shape  of  horizontal  strata,  evidently 
deposited  by  sedimentation  or  biologic  growths  at  a  time  when  the 

*  Sodium,  potassium,  and  certain  less  common  chemical  elements  are 
known  as  the  metals  of  the  alkalies.  Calcium,  magnesium,  and  certain  less 
common  elements  having  similar  properties  are  known  as  the  metals  of  the 
alkaline  earths.  The  presence  of  both  alkaline  and  alkaline  earths  compounds 
contributes  to  the  property  of  water  called  "  alkalinity,"  while  only  the 
alkaline  earths  compounds  contribute  toward  the  property  of  "  hardness." 


6  WATER  PURIFICATION   PLANTS 

land  was  submerged  beneath  the  sea.  Such  formations  are  the 
limestones,  dolomite  (mixed  calcium  and  magnesium  carbonate), 
sandstones,  and  shales,  which  form  the  great  central  valley  of  the 
United  States,  as  well  as  the  more  localized  beds  of  salts  (sodium, 
calcium,  and  magnesium  chlorids),  gypsum  (calcium  sulphate),  etc. 
Again,  large  areas  are  deeply  covered  by  till  formed  of  finely 
comminuted  rock  material  interpersed  with  bowlders,  which  has 
resulted  from  glacial  action.  In  the  northern  United  States  a  large 
sheet  of  this  material  exists,  covering  roughly  the  Dakotas,  Minne- 
sota, Wisconsin,  Michigan,  Iowa,  Illinois,  Indiana,  most  of  New 
York,  New  England  and  part  of  Ohio,  Nebraska,  Kansas,  and 
Missouri.  In  part  it  consists  of  gravels,  sand,  and  clay,  but  con- 
tains much  ground-up  limestone  and  dolomite,  so  that  it  may  be 
said  to  act  the  same  as  strata  of  these  toward  the  percolating 
water,  the  resulting  ground  water  being  high  in  bicarbonates  of 
calcium  and  magnesium. 

The  water  passing  through  such  secondary  formations  dissolves 
the  carbonates  present  by  virtue  of  its  contained  carbonic  acid, 
and  removes  them  as  bicarbonates.  Thus  in  the  case  of  calcium- 
and  magnesium  carbonates  the  reaction  is : 

CaCO3  +  H2CO3  =  CaCO3,H2C03 
MgCO3  +  H2C03  =  MgCO3,H2CO3 

These  bicarbonates  give  to  a  water  the  property  of  temporary 
hardness,  so  called  because,  by  heating,  the  carbonic  acid  is  driven 
off,  and  the  normal  carbonates  are  precipitated. 

The  existence  of  large  deposits  of  salt  and  gypsum  has  been 
mentioned.  Water  passing  through  such  formations  acquires 
considerable  amounts  of  these  compounds  as  sodium  and  calcium 
chlorids  (NaCl  and  CaCl2),  and  as  calcium  sulphate  (CaS04), 
respectively.  Magnesium  sulphate  (MgSOJ  is  also  acquired  in 
this  way.  These  render  the  water  permanently  hard,  i.e.,  the 
hardness  cannot  be  removed  by  ordinary  boiling.  A  stream  may 
also  have  its  chlorid  content  increased  by  the  discharges  from  oil 
and  brine  wells,  and,  if  near  the  sea,  by  salt  spray  carried  inland 
on  the  winds.  Decomposing  organic  matter  is  another  source  of 
chlorids  in  water.  Most  limestones  contain  small  amounts  of 
calcium  sulphate,  so  that  it  is  quite  generally  found  in  secondary 
waters. 

If  an  alkaline  stream  mingles  with  one  containing  sulphates 


WATER   AND    ITS   IMPURITIES  7 

and  chlorids  of  calcium  and  magnesium,  a  softening  reaction 
results  quite  similar  to  the  artificial  process,  with  the  formation 
of  sulphates  and  chlorids  of  sodium  and  potassium,  and  the 
precipitation  of  calcium  and  magnesium  as  carbonates  or 
their  retention  as  bicarbonates,  according  to  the  following 
equations  : 

CaS04  1       9MQ  pn          f  CaC03 
MgS04j+  2Na2C°3  =:      MgC03 

H 


{MgC03j 


This  accounts  for  the  large  amounts  of  sodium  sulphate  sometimes 
found  in  primary  waters. 

Traces  of  the  nitrates  of  alkalies  and  alkaline  earths  exist  in 
various  rocks,  and  these  find  their  way  into  the  water  and  enter 
into  reactions  in  a  manner  quite  similar  to  the  sulphates  and 
chlorids. 

Iron  is  quite  abundant  and  almost  universally  distributed, 
occurring  in  most  rock  formations,  and  especially  in  gravels  and 
sands,  which  often  have  a  distinct  yellow  or  reddish  discoloration 
as  a  result.  It  occurs  most  commonly  as  hematite  (Fe2O3). 
As  has  been  stated,  water  is  often  deprived  of  its  oxygen  by 
decaying  organic  matter,  in  passing  through  the  soil.  In  this 
condition  it  will,  if  it  comes  in  contact  with  iron  oxid,  remove 
from  the  latter  part  of  the  oxygen,  leaving  it  as  ferrous  oxid  (FeO)  . 
This  ferrous  oxid  combines  with  the  carbonic  acid  in  the  water  to 
form  the  soluble  ferrous  bicarbonate  (Fe(HCO3)2),  which  is 
carried  off  in  solution.  Many  waters  contain  a  trace  of  iron  in 
this  form.  When  a  badly  polluted  stream  devoid  of  oxygen 
flows  over  or  percolates  through  a  gravel  bed,  or  when  the  under- 
flow of  such  a  stream  is  tapped  by  means  of  wells,  the  water  be- 
comes so  highly  charged  with  iron  as  to  become  unusable.  Simi- 
larly a  subterranean  supply  drawn  from  a  gravel  bed  is  usually 
high  in  iron.  On  standing,  exposed  to  the  air,  an  iron-containing 
water  will  become  turbid,  due  to  the  oxidation  of  the  iron,  which 
is  changed  to  the  insoluble  ferric  hydroxid  (Fe(OH)3).  The  iron 
bacterium,  Crenothrix,  subsists  on  the  soluble  ferrous  carbonate 
and  changes  it  into  an  insoluble  ferric  state,  leaving  it  in  the  water 
as  a  stringy,  gelatinous  precipitate.  This  bacterium  grows  with- 


8  WATER   PURIFICATION   PLANTS 

out  light,  consequently  thrives  in  covered  reservoirs,  water  mains, 
and  the  like.  Iron  sulphate  occurs  in  mine  waters  and  will  be  dis- 
cussed later. 

Of  the  gases  contained  in  water,  the  most  common  are  carbonic 
acid  (CO2),  oxygen,  and  nitrogen.  The  former  is  derived  from  the 
air,  from  decaying  vegetation  and  plant  excretion  in  the  soil,  and 
from  decaying  organic  matter  in  lakes,  swamps,  and  quiescent 
bodies  of  water  generally.  Oxygen  is  derived  mainly  from  the 
air.  These  gases  are  acquired  from  the  air  quite  rapidly,  so  that 
if  the  water  is  for  any  reason  depleted,  a  fresh  supply  is  soon  ob- 
tained. There  is  some  question  as  to  how  this  repletion  takes 
place.  In  event  of  wave  action,  rapids,  or  cascades,  the  method 
is,'  plainly  enough,  one  of  mechanical  mixture,  followed  by  the 
solution  of  the  gases  in  the  water.  In  the  case  of  quiet  bodies  of 
water,  the  process  is  less  plain.  It  is  contended  by  some  that  the 
gases  are  dissolved  in  the.  surf  ace  water  by  contact,  and  pass  into 
the  interior  of  the  water  by  diffusion,  which  is  the  tendency  of 
soluble  bodies  in  solution  so  to  distribute  through  the  solvent  that 
the  concentration  will  be  uniform  throughout.  Thus,  a  gas 
dissolved  in  the  surface  of  a  liquid  would  distribute  itself  through- 
out the  body  thereof  so  as  to  bring  about  a  uniform  distribution  of 
the  gas  particles.  This  theory  is  opposed  with  much  validity  by 
the  contention  that  the  rate  of  diffusion  is  too  slow  to  account  for 
the  rapid  replenishment  which  actually  occurs.  The  opponents 
advance  the  theory  of  "  streaming  action,"  according  to  which 
evaporation  from  the  surface  layer  concentrates  the  impurities  in 
it,  causing  it  to  become  of  higher  specific  gravity  than  the  water 
below,  and  to  sink,  carrying  down  the  occluded  gases  obtained  by 
contact  with  the  air.  In  lakes  and  swamps  abounding  in  plant 
life  a  balanced  relation  between  carbonic  acid  and  oxygen  has 
been  found  to  exist.  During  the  growing  season,  carbonic  acid  is 
absorbed  by  the  plants,  and  oxygen  is  given  off,  causing  the  water 
to  be  high  in  oxygen  and  deficient  in  carbonic  acid.  During  the 
dormant  period  of  plant  life  the  reverse  is  true.  Plants  will  first 
use  up  the  free  carbonic  acid  in  the  water,  and  thereafter  the  half- 
bound  carbonic  acid,  which  is  in  loose  combination  as  the  bicar- 
bonates  of  calcium  and  magnesium,  causing  these  to  precipitate 
as  normal  carbonates.  It  follows  that  during  the  growing  season, 
the  alkalinity  and  temporary  hardness  of  the  water  are  reduced. 
The  presence  of  a  trace  of  carbonic-acid  gas  seems  to  render  water 


WATER   AND    ITS   IMPURITIES 


9 


more  palatable,  probably  because  it  is  a  natural  content  of  normal 
waters. 

All  normal  waters  contain  oxygen  in  considerable  concentra- 
tion, usually  over  50  per  cent  of  the  saturation  value,  and  it  is 
only  deficient  in  waters  polluted  by  putrescible  organic  matter,  or 
containing  oxidizable  mineral  matter  (such  as  mine  drainage). 
Waters  not  charged  with  sufficient  oxygen  give  off  disagreeable 
odors  and  will  not  support  fish  life,  and  are  shunned  as  water 
supplies. 

Nitrogen  is  absorbed  from  the  air  in  the  same  manner  as  oxygen, 
but  is  an  inert  gas  chemically.  Methane  (marsh  gas)  is  found  in 
swanip  water,  due  to  decayed  vegetation.  Hydrogen  sulphid  is 
found  in  presence  of  decaying  organic  matter  and  in  some  deep 
well  waters.  The  last  two  gases  are  conspicuous  because  of  the 
unpleasant  taste  and  odor  which  they  impart  to  the  water.  They 
can  be  removed  to  a  large  extent  by  aeration. 

The  saturation  value  of  all  gases  in  water  varies  with  the 
temperature.  Table  I  shows  these  variations  for  oxygen,  from 
which  it  is  seen  that  the  concentration  increases  with  lower 
temperatures. 

TABLE  I* 

QUANTITIES  OF  DISSOLVED  OXYGEN  IN  PARTS  PER  MILLION  BY  WEIGHT  IN 
WATER  SATURATED  WITH  AIR  AT  THE  TEMPERATURE  GIVEN 


Temp.  C.            Oxygen 

Temp.  C. 

Oxygen 

Temp.  C. 

Oxygen 

0 

14.70 

11 

11.05 

21 

9.01 

1 

14.28 

12 

10.80 

22 

8.84 

2 

13.88 

13 

10.57 

23 

8.67 

3 

13.50 

14 

10.35 

24 

8.51 

4 

13.14 

15 

10.14 

25 

8.35 

5 

12.80 

16 

9.94 

26 

8.19 

6 

12.47 

17 

9.75 

27 

8.03 

7 

12.16 

18 

9.56 

28 

7.88 

8 

11.86 

19 

9.37 

29 

7.74 

9 

11.58 

20 

9.19 

30 

7.60 

10 

11.31 

*  Standard  Methods  of  Water  Analysis — American  Public  Health  Association. 

As  has  been  said,  the  water  in  a  stream  is  of  two  components — 
the  surface  runoff  and  the  ground-water  supply.  The  first  com- 
ponent furnishes  the  flood  flows  and  the  turbidity,  the  second 
feeds  the  stream  uniformly  with  a  mineralized  water,  consequently 
supplies  the  low-water  flow  of  the  stream  almost  entirely.  It 


10  WATER   PURIFICATION   PLANTS 

results  that  during,  high  water  the  mineral  content  of  the  water  is 
low  while  during  low  water  it  is  high.  Furthermore,  the  under- 
flow of  a  stream  generally  carries  more  dissolved  mineral  matter 
than  the  surface  flow.  During  floods  the  carbonic  acid  and  organic 
matter  in  the  water  may  increase,  due  to  flushing  out  of  back- 
channels,  stagnant  pools,  and  swamps. 

Water  from  streams  draining  areas  of  primary  rock,  sand,  or 
other  resistant  material  are  very  often  colored.  This  is  not  due  to 
turbidity,  which  gives  to  water  an  apparent  color  depending  on  the 
kind  of  sediment  carried,  but  to  coloring  matter  in  solution,  which 
cannot  be  removed  by  ordinary  filtration.  This  coloring  matter  is 
derived  from  decaying  vegetable  matter  in  swamps,  or  from  muck 
and  peat  beds.  It  consists  generally  of  tannates,  gallates,  and 
organic  acids  from  the  leaves  and  bark  of  shrubs  and  plants. 
Turbid  waters  are  not  generally  colored,  since  the  clay  carried  as 
sediment  is  partly  in  the  colloidal  state  and  has  the  power  of  re- 
moving color  by  the  process  of  adsorption,  by  which  the  colloidal 
particles  draw  the  color  into  themselves,  as  a  sponge  does  water. 
The  efficacy  of  this  process  depends  upon  the  type  of  clay  con- 
stituting the  turbidity,  impure  clays  being  best. 

Thus  far,  only  the  properties  of  normal  or  natural  waters  have 
been  considered.  In  some  cases  industrial  wastes  modify  or 
completely  change  the  character  of  streams.  Most  notably  is  this 
the  case  with  streams  receiving  mine  drainage,  especially  from  coal 
mines.  Coal  contains  sulphur  in  the  form  of  calcium  sulphate, 
as  iron  pyrites  (FeS2),  and  probably  in  organic  form.  This  is 
discharged  in  the  mine  drainage  as  sulphuric  acid  (H2SO4)  and 
ferrous  sulphate  (FeSOJ. 

On  reaching  the  stream,  the  ferrous  sulphate  is  oxidized  by  the 
oxygen  contained  in  the  water,  forming  ferric  hydroxid,  which 
settles  out,  and  ferric  sulphate,  which  remains  in  solution: 
6FeS04  +  3O  +  3H2O  =  2Fe2(SO4)3  +  Fe2(OH)6 

Fe2(OH)6  =  Fe2O3  +  3H2O 

The  rate  of  oxidation  is  partly  dependent  on  the  replenishment  of 
the  air  supply  in  the  water.  Under  the  most  favorable  conditions 
of  oxygen  supply  the  process  consumes  several  days,  so  that  water 
in  mining  regions  may  contain  sulphuric  acid  and  both  ferrous 
and  ferric  sulphates.  As  limestones  are  present  in  coal-bearing 
formations,  the  normal  streams  of  such  regions  would  contain 
bicarbonates  of  calcium  and  magnesium,  but  the  iron  sulphates 


WATER   AND    ITS   IMPURITIES  11 

and  sulphuric  acid  react  with  these,  and  calcium  and  magnesium 
sulphates  result,  together  with  iron  carbonate,  which,  if  sufficient 
oxygen  is  present,  is  precipitated  as  hydroxid.  Thus  a  mine  water 
will  contain  the  constituents  of  permanent  hardness,  and,  with  in- 
creasing mine-drainage  factor,  ferrous  and  ferric  sulphate  and 
finally  sulphuric  acid.  Where  the  mine  drainage  is  of  recent 
addition  paucity  of  oxygen  and  the  presence  of  ferrous  carbonate 
will  be  noticeable. 

The  most  objectionable  property  of  water  containing  mine 
drainage  is  its  corrosiveness.  The  iron  sulphates  and  acid  will 
actively  attack  metals.  A  limited  quantity  of  ferric  sulphate, 
once  admitted  into  a  boiler  or  other  closed  metallic  water  con- 
tainer, will  attack  the  same  unintermittently.  The  ferric  sulphate 
will  dissolve  sufficient  iron  to  reduce  itself  to  the  ferrous  condition, 
and  being  oxidized  by  the  air  admitted  with  fresh  water,  will  again 
attack  the  boiler,  and  by  continuous  repetitions  of  this  process 
will  accomplish  its  early  ruin.  Brass  piping,  plumbing  fixtures, 
etc.,  are  eaten  away,  and  even  "  acid-proof  "  bronze  is  not  immune. 
Other  objectionable  qualities  are  the  taste  imparted  and  dis- 
coloration in  laundry  work.  In  the  stream  itself  the  lack  of  dis- 
solved oxygen  is  harmful  and  often  prohibitive  to  fish  life,  but  no 
bad  odors  are  caused  by  decomposing  organic  matter,  as  should 
be  expected  in  deoxidized  water,  because  the  iron  sulphates  pre- 
cipitate organic  matter  as  non-putrefactive  compounds.  Such 
waters  are  comparatively  free  from  bacteria,  which  cannot  live 
under  very  acid  conditions.  If,  however,  the  exposure  to  acid 
water  is  short,  they  may  form  spores.  It  thus  sometimes  happens 
during  the  purification  of  acid  water  that  the  raw  water  seems 
sterile,  but  when  treated  with  lime  and  settled,  numerous  colonies 
of  bacteria  appear,  due  to  development  of  the  spores  under  favor- 
able alkaline  conditions.  Acid  water  will  cause  sediment  in  sus- 
pension to  coagulate,  so  that  in  a  turbid  stream,  on  entering  a 
mining  region,  the  suspended  matter  will  collect  in  clots,  and  later 
settle  out,  leaving  the  water  clear.  Should  a  stream  containing 
ferrous  sulphate  mingle  with  one  high  in  color,  due  to  vegetable 
tannates  and  gallates,  the  water  will  become  black,  due  to  the 
formation  of  natural  ink.* 

While  mine  drainage  is  the  most  important  industrial  waste  in 

*  Proc.  Eng.  Soc.  Western  Penna.,  Vol.  XXVII,  No.  8. 


12  WATER   PURIFICATION    PLANTS 

changing  the  character  of  streams,  other  wastes  may  have  a 
marked  but  more  localized  effect.  Drainage  from  salt  and  oil 
wells  may  so  pollute  a  stream,  especially  if  small,  as  to  render  it 
unfit  for  use,  and  even  large  rivers  may  acquire  a  briny  taste  from 
this  source.  About  250  parts  per  million  of  chlorine  will  give 
water  a  salty  taste.  The  salt  further  deposits  in  boilers,  forming 
scale.  Tannery  waste  imparts  a  color  to  the  water,  and,  due  to 
acids  present,  has  a  germicidal  effect,  although  not  generally 
strong  enough  to  kill  the  spores.  Paper-mill  waste  consists 
partly  of  vegetable  organic  matter  and  of  spent  acid  and  bleach 
liquors.  Other  sources  of  pollution  are  dye  works,  steel  mills 
(pickling  acids),  slaughter-houses,  and  breweries.  The  last  two 
may  have  an  important  influence  where  a  water  supply  is  obtained 
from  wells  in  alluvial  drift.  They  impart  much  organic  matter 
to  the  water,  whose  putrefaction  deprives  it  of  oxygen,  so  that  the 
water  in  percolating  through  the  alluvial  gravel  becomes  very 
highly  charged  with  iron,  and  unfit  for  use. 

Sewage  from  towns  and  cities  is  an  important  source  of  pollu- 
tion, particularly  because  through  it  such  diseases  as  typhoid  fever, 
cholera,  etc.,  are  disseminated.  The  sewage  contains  much  nitrog- 
enous organic  matter  in  solid  (finely  divided)  and  colloidal  states 
and  in  solution,  as  well  as  large  numbers  of  sewage  bacteria 
(which  may  average  3,000,000  per  cubic  centimeter  and  more). 
Through  the  agency  of  some  of  these  bacteria,  the  organic  matter 
absorbs  the  dissolved  oxygen  from  the  water  of  the  stream  into 
which  the  sewage  discharges,  and  is  oxidized,  with  the  production 
of  carbonic  acid,  water,  and  salts  of  nitrogen.  Other  bacteria 
attack  the  solid  and  colloidal  organic  matter,  reducing  it  to 
solution,  and  by  a  process  of  fermentation  break  it  up  into  ammonia, 
hydrogen  and  hydrogen  sulphid,  nitrogen,  and  marsh  gas.  By 
further  oxidation,  the  ammonia  is  changed  to  nitrites  and,  finally, 
to  stable  nitrates.  Physically,  sewage  pollution  may  impart  to  the 
water  a  turbid  appearance  varying  with  large  amounts  from  milky 
white  to  almost  black,  according  to  the  amount  of  putrescible 
matter;  strong  odors,  due  to  putrefaction;  and  innumerable  bac- 
teria. Chemically,  it  is  evidenced  by  the  scarcity  of  dissolved 
oxygen  and  by  the  presence  of  ammonia,  carbonic  acid,  nitrites 
and  nitrates.  The  indicative  tests  are  those  for  albuminoid 
ammonia  (due  to  very  recent  pollution  and  the  presence  of  un- 
oxidized  nitrogenous  matter),  free  ammonia  (evidence  of  partially 


WATER   AND    ITS    IMPURITIES  13 

decomposed  sewage,  and,  consequently,  more  remote  pollution), 
nitrites,  and  nitrates,  the  final  decomposition  products  in  stable 
inorganic  form.  Sewage  is  high  in  chlorine,  but  this  passes  un- 
changed through  the  various  stages  of  putrefaction  and  affords  no 
reliable  evidence  of  the  tune  of  pollution. 

The  living  world  is  largely  represented  in  natural  water.  Of 
plant  forms,  besides  such  higher  plants  as  water  lilies,  water  ferns, 
etc.,  there  is  a  large  representation  of  free  floating  types,  the 
group  Thallophytes  being  most  prominent.  This  group  has  two 
great  divisions  Algce  and  Fungi.  In  the  first  division  are  in- 
cluded the  masses  of  green  floating  filaments,  blue-green  alga? 
(Cyanophyceae),  so  commonly  seen  in  ponds  and  reservoirs,  which 
impart  grassy  odors  to  the  water,  and  the  pond  scum,  or  green 
algae  (Chlorophycese).  Also  the  minute,  one-celled  plant  forms 
(diatoms),  which  may  be  either  free-swimming  (having  the  power 
of  motion)  or  attached  by  gelatinous  stalks,  and  which  give  off 
strong  odors,  especially  in  the  spring  and  fall.  The  peculiarity  of 
the  Algae  is  their  ability  to  subsist  on  inorganic  matter,  being 
true  plants.  The  Fungi,  however,  are  parasitic,  and  can  only  live 
on  organic  matter.  Such  are  water  molds  and  bacteria  (Schizo- 
my  cetes) . 

Bacteria  are  microscopic,  one-celled  fungi,  which  generally  have 
the  power  of  motion.  They  are  very  numerous  in  water,  and  de- 
rived from  several  sources.  Many  species  are  indigenous  to  water; 
others  are  soil  bacteria  which  have  been  washed  into  the  stream, 
and  these  predominate  during  floods  and  in  turbid  waters.  Sewage 
contributes  others,  each  cubic  centimeter  containing  many  mil- 
lions. Most  bacteria  in  the  water  are  harmless  or  beneficial, 
assisting  in  the  decomposition  of  organic  matter,  but  some  species 
contained  in  sewage  are  very  harmful,  being  capable  of  producing 
disease,  if  the  water  is  used  for  drinking  purposes.  These  diseases 
are  mainly  intestinal  in  character,  and  are  transmitted  by  the  dis- 
charges of  patients  entering  streams  as  part  of  the  sewage,  the 
bacteria  being  disseminated  through  the  water,  which  is  drunk 
by  other  persons  further  down  stream.  The  most  common  are 
typhoid  fever,  cholera,  dysentery,  diarrhoea,  and  other  intestinal  dis- 
turbances. The  bacteria  of  these  diseases  do  not  grow  or  multiply 
in  the  water,  which  acts  simply  as  a  carrier.  They  arc,  in  fact, 
very  difficult  to  discover  or  isolate  in  a  water  supply,  but  there 
exists  a  group  of  bacteria,  the  Coli  bacilli,  which  flourish  only  in  the 


14 


WATER    PURIFICATION    PLANTS 


V-""1 


,- 


Bacillus  Typhosus 

XIOOO 
Flagellated  Form  on  left 


B.  Coll  Communis 

xiooo 


<>'<<> 


Cholera 
X2000 


Blue-Green  Algae 
X100 


ee  Swimming  Spores 


Diatoms  (Top  View) 
X30 


Paramaecia 
X30 


FIG.    1. — Microscopic   Life   in   Water.     The   number   below   each 
group  indicates  the  degree  of  magnification. 


WATER  AND   ITS   IMPURITIES 


15 


intestines  of  man  and  higher  animals,*  are  readily  detected  and 
identified,  and  are  therefore  considered  indicative  of  human  or 
animal  pollution.  Their  evidence  has  great  sanitary  value,  as  a 
water  receiving  human  excreta  may  at  any  time  receive  that  of  a 
sufferer  from  typhoid  tir  other  intestinal  diseases. 

As  to  the  representatives  of  animal  life,  besides  fish  and  the 
higher  forms  there  are,  among  others,  fresh-water  sponges  (Spon- 
gid®),  minute,  free-swimming  shrimp-like  forms  (Crustacea),  and 
Protozoa.  The  last  are  microscopic  unicelled  animalcules,  which 
seem  quite  closely  related  to  bacteria  in  form  and  habits.  Both 
sponges  and  protozoa  may  cause  tastes  and  odors  in  water. 

As  this  discussion  of  the  properties  of  water  has  been,  in  the 
main,  qualitative,  it  may  be  well  in  closing  to  give  a  few  quantita- 
tive examples  of  water  types,  so  that  the  reader  may  form  an  idea 
of  the  proportions  in  which  the  various  constituents  exist : 

TABLE  II 
TYPICAL  WATERS:  ANALYSES  IN  PART  PER  MILLION 


Compounds 

A 

B 

C 

D 

E 

Sodium  Sulphate  

6 

9 

6 

4 

16 

Potassium  Sulphate  

2 

3 

Calcium  Sulphate  

57 

68 

78 

Magnesium  Sulphate 

33 

Iron  Sulphate  

12 

Sulphuric  Acid 

40 

Sodium  and  Potassium  Chlorid  

4 

5 

8 

51 

7 

Calcium  Chlorid    . 

23 

Sodium  and  Potassium  Nitrate  
Sodium  and  Potassium  Carbonate 

1 
6 

4 

7 

6 

2 

Bicarbonate  of  Iron  

2 

2 

1 

1 

Sodium  and  Potassium  Bicarbonate  

15 

Calcium  Bicarbonate  

25 

130 

170 

117 

Magnesium  Bicarbonate.  

11 

49 

135 

96 

Silica  

28 

15 

17 

17 

9 

Alumina  

8 

A.  Stream  flowing  through  primary  formation.  The  car- 
bonates and  bicarbonates  of  the  alkalies  are  high,  those  of  the 
alkaline  earths  low.  The  water  received  some  calcium  and 
magnesium  sulphate,  which  reacted  with  the  alkaline  carbonates 
to  form  alkaline  sulphates,  with  a  corresponding  increase  in  the 


*  For  a  modification  of  this  statement,  see  page  141. 


16  WATER   PURIFICATION    PLANTS 

bicarbonates  of  the  alkaline  earths.     Note  the  high  silica  content 
(in  colloidal  state). 

B.  Typical    secondary    stream,    from     limestone    formation. 
The  principal  constituents  are  alkaline  earth  bicarbonates.     A 
small  amount  of  alkaline  carbonates  was  present,  as  well  as  some 
calcium  or  magnesium  sulphate,   which  by  interaction  formed 
sodium  sulphate  and  alkaline  earth  bicarbonates.     In  this  water 
all  hardness  is  temporary  and  equals  the  total  alkalinity. 

C.  Stream  high  in   calcium  sulphate   (permanent    hardness). 
This  water  is  characterized  by  permanent  hardness  and  a  high 
magnesium  content. 

D.  Stream  high  in  chlorids.     Polluted  by  salt  wells  or  mines. 

E.  A  stream  badly  polluted  by  mine  water.     This  was  normally 
a  water  of  type  C,  although  lower  in  bicarbonates,  but  has  been 
entirely  changed  in  character  by  the  action  of  iron  sulphate  and 
sulphuric  acid  from  mine  drainage,  almost  all  constituents  being 
converted  into  sulphates.     An  extension  of  the  analysis  to  dis- 
solved gases  would  probably  show  much  carbonic  acid  and  a  de- 
ficiency of  oxygen.     The  alumina  in  solution  is  characteristic  of 
such  waters. 

Note  in  all  the  analyses:  (a)  the  uniformity  of  the  chlorids 
(except,  of  course,  in  D);  (6)  the  uniformity  of  nitrates,  iron 
(except  in  E),  and  silica  (except  in  A),  suggesting  that  these 
constituents  are  more  or  less  equally  distributed  through  all 
geological  formations  and  are  sluggish  chemically  in  the  form 
present. 

Fig.  2  shows  a  map  of  the  United  States  on  which  the  geological 
formations  are  very  broadly  indicated.  The  principal  primary 
formations  are  in  the  Appalachians,  the  northern  part  of  Wis- 
consin and  Minnesota,  and  the  great  mountain  region  of  the  West. 
A  large  area  of  central  and  northern  United  States,  roughly  that 
portion  north  of  the  Missouri  and  Ohio  Rivers,  is  deeply  covered 
with  glacial  drift,  which  in  some  cases  consists  of  ground-up  local 
rock,  and  in  others  of  materials  transported  hundreds  of  miles 
from  their  original  locations.  Some  of  this  material  has  also  been 
carried  south  of  the  area  of  glaciation  by  prehistoric  torrents,  and 
by  the  rivers  and  winds.  Streams  in  this  glaciated  region  derive 
many  of  their  mineral  qualities  from  the  leaching  of  this  drift. 
The  limestone  formation  occuring  in  Missouri,  Kentucky,  southern 
Ohio,  Tennessee,  Alabama,  and  Georgia  is  also  indicated.  The 


WATER    AND    ITS    IMPURITIES 


17 


FIG.  2. — Map  to  Illustrate  how  Geologic  Formations  Influence  the 
Properties  of  Water. 


18  WATER   PURIFICATION    PLANTS 

streams  of  this  formation  are  notoriously  hard,  and  require  soften- 
ing for  economical  use.  Areas  polluted  by  mine  drainage  are 
shown  in  black.  The  map  illustrates  the  heterogeneous  chemical 
contents  to  be  expected  in  large  rivers.  Thus  the  Missouri 
originates  in  an  area  of  primary  rocks,  later  flows  through  a  region 
of  secondary  or  derivative  formation,  receiving  also  its  quota  of 
hard  water  from  limestone  beds.  This  map  is  submitted,  to  illus- 
trate broadly  the  principles  involved  and  makes  no  pretense  at 
great  accuracy  or  detail. 


CHAPTER  II 

TYPES  OF  PURIFICATION  PLANTS 

THE  objects  of  water  purification  may  be  briefly  stated  as 
follows: 

1.  To  render  the  water  safe  and  harmless  for  drinking  and 
domestic  use.     This  involves  the  almost  complete  removal  of 
bacteria,  in  order  to  be  sure  that  all  uathogenic  (disease-producing) 
species  are  eliminated. 

2.  To  make  the  water  inviting  and  pleasing  in  appearance  and 
taste.     This  requires: 

(a)  The  removal  of  suspended  matter. 

(6)  The  removal  of  odors  and  tastes. 

(c)  The  elimination  of  dissolved  color. 

(d)  The  removal  or  oxidation  of  organic  matter. 

(e)  The  removal  of  iron. 

3.  Improving  the  water  for  industrial  and  household  use  by: 
(a)  Reducing  the  hardness  (temporary  and  permanent). 
(6)  Eliminating  iron  in  solution. 

(c)   Neutralizing  acids  (such  as  sulphuric  and  carbonic). 

Any  or  all  of  these  objects  are  attainable  by  means  of  a  proper- 
ly designed  and  operated  purification  plant  to  a  degree  sufficient 
to  meet  all  requirements.  It  is  possible  to  remove  over  99  per  cent 
of  the  bacteria  regularly,  and  by  sterilization  the  removal  may  be 
made  practically  complete.  It  is  hardly  necessary  to  say  that 
this  has  a  marked  effect  on  the  reduction  of  water-borne  diseases, 
but  it  may  be  well  to  call  attention  to  Fig.  3,  showing  the  death- 
rate  from  typhoid  fever  in  Columbus,  Ohio,*  for  the  last  ten  years, 
during  five  of  which  the  water  was  filtered.  Filtering  has  reduced 
the  death-rate  from  an  average  of  about  75  per  100,000  to  about  17 
per  100,000  per  year.  The  reduction  in  typhoid  fever  is  further 
shown  by  the  following  table,  compiled  by  Mr.  Allen  Hazen: 


*  Compiled  by  Charles  P.  Hoover,  Chemist  in  Charge  of  Filtration  Plant, 
Columbus,  O. 

19 


20 


WATER   PURIFICATION   PLANTS 


TABLE  III 

ANNUAL  AVERAGE  DEATH-RATES  FROM  TYPHOID  FEVER  BEFORE  AND  AFTER 

FILTRATION 


City 

EXTENT  OF  RECORD 

TYPHOID  DEATH-RATES 
PER  100,000 

Years  Before 

Years  After 

Before 

After 

Binghamton,  N.  Y.  .  .  . 

5 
4 
11 
7 
5 
5 
2 
9 
7 
5 

5 
4 
4 
6 
9 
7 
12 
9 
15 
6 

47 

50 
78 
19 
32 
100 
76 
74 
114 
57 

15 
12 
11 
14 
10 
32 
21 
22 
25 
33 

Cincinnati,  O  

Columbus.  O  

Hoboken,  N.  J  

Paterson,  N.  J  

Watertown  N  Y. 

York,  Pa 

Albany,  NY* 

Lawrence,  Mass.*                .  .  . 

Washington,  D.  C.*  

*  Slow  sand  niters. 

From  Hazen,  in  International  Congress  of  Demography  and  Hygiene,  1912. 


TYPHOID  FEVER  DEATH   RATE 
PER  100,000  POPULATION 
COLUMBUS,  OHIO 

150 

1904 

1905 

1906 

1907 

1908 

1909 

1910 

1911 

1912 

1913 

150 

125 

125 

100 

100 

75 

75 

50 

50 

25 

25 

• 

• 

• 

0 

• 

0 

• 

• 

• 

• 

• 

• 

• 

• 

UNFILTERED  WATER 

FILTERED  WATER 

FIG.  3.— An  Example  of  the  Decrease  in  Typhoid  Fever  Death-Rate  Fol- 
lowing Filtration  of  the  Water  Supply. 


TYPES    OF    PURIFICATION    PLANT6  21 

Suspended  matter  can  be  completely  removed;  odors,  tastes, 
and  color  can  be  greatly  reduced.  Hardness  can  be  reduced  to 
the  residuum  due  to  dissolved  carbonates,  and  the  same  may  be 
said  of  acids,  if  the  treatment  is  carried  far  enough.  Iron  and 
organic  matter  can  be  brought  down  to  negligible  quantities. 

The  processes  of  water  purification  rinding  practical  applica- 
tion for  municipal  purposes  are: 

(a)  Coagulation  and  sedimentation. 

(b)  Slow  sand  filtration. 

(c)  Rapid  sand  or  mechanical  filtration. 

To  these  might  be  added  filtration  through  natural  sand  beds, 
possible  only  under  exceptional  geological  conditions,  and  various 
experimental  methods  of  unproven  value. 

Coagulation  and  Sedimentation.  Coagulation  and  sedimen- 
tation is  used  to  some  extent  in  purifying  the  turbid  river  waters 
of  the  Middle  West,  and  has  found  its  most  successful  application 
at  St.  Louis,  Mo.,*  and  a  number  of  other  municipalities  situated 
on  the  Missouri  River.  It  requires  coagulating  apparatus  and 
facilities  of  the  kind  described  in  connection  with  mechanical 
filtration,  and  large  settling  basins,  of  from  one  to  three  days' 
capacity. 

The  coagulants  used  are  generally  ferrous  sulphate  and  lime, 
owing  to  their  comparative  cheapness  and  the  high  specific  gravity 
of  the  coagulum  formed.  As  the  waters  thus  treated  are  very 
turbid,  large  amounts  of  coagulants  are  required,  and  for  the  same 
reason  the  question  of  organic  coloring  matter,  a  delicate  subject 
in  connection  with  the  iron-lime  treatment,  is  eliminated.!  Alum 
and  lime  as  coagulants  have  also  been  used  in  this  process. 

The  settling  basins  are  similar  to  those  described  in  connection 
with  mechanical  filtration,  except  in  respect  to  size.  Needless  to 
say,  the  study  of  proper  baffling  in  order  to  prevent  short-circuit- 
ing or  currents  is  of  utmost  importance  in  this  case.  It  is  not 
likely  that  this  process  will  find  extensive  use  in  the  future,  as 
mechanical  filtration  has  proven  to  be  more  effective  and  eco- 
nomical. The  general  tendency  is  toward  supplementing  with 
filtration  such  plants  as  are  now  in  operation. 

*  The  process  at  St.  Louis  has  been  supplemented  by  mechanical  filtration, 
t  See  page  243. 


22  WATER    PURIFICATION    PLANTS 

The  data  and  charts  in  this  book  apply  with  equal  force  to  this 
process,  as  does  also  much  of  the  matter  in  the  last  chapter,  despite 
the  title  thereof. 

Slow  Sand  Filtration.  This  process  is  of  English  origin,  and 
dates  from  about  1830.  From  England  it  was  disseminated 
throughout  the  Continent,  where  it  is  now  widely  used.  In 
America  it  has  found  extended  use  in  the  older  installations  and 
in  the  purification  of  the  supplies  of  large  cities,  although  of 
recent  years  the  mechanical  process  has  become  an  important 
competitor  in  plants  of  large  size,  and  has  far  outstripped  it  in  the 
case  of  supplies  for  smaller  towns. 

Description  of  Plant.  A  general  view  of  a  typical  slow  sand 
filtration  plant  is  shown  by  Fig.  4.  It  consists  of  duplicate  sedi- 
mentation basins  d-d,  the  filter  units  g-g-g,  the  office  and  labora- 
tory e,  and  various  auxiliaries. 

The  water  is  drawn  from  the  river  through  the  intake  a,  and 
pumped  to  the  sedimentation  basins  by  low-service  pumps  in  the 
station  6,  entering  the  basins  through  a  distributing  grid  of  pipe 
which  may  terminate  in  the  aerating  risers  c-c-c,  to  remove  ob- 
noxious gases  from  the  water,  and  distribute  it  uniformly  across 
the  basins.  It  is  sometimes  desirable  with  turbid  waters  to  use 
coagulants  to  assist  in  clarification,  in  which  case  the  necessary 
apparatus,  similar  to  that  used  in  mechanical  filtration,  is  in- 
stalled in  the  building  e,  which  is  enlarged  for  that  purpose  and 
for  coagulant  storage.  The  size  of  the  basins  is  dependent  on  the 
amount  and  fineness  of  sediment  in  the  raw  water,  the  period  of 
sedimentation  being  generally  from  four  to  twelve  hours.  In 
filtering  clear  lake  water,  where  the  removal  of  bacteria  is  the  main 
object,  the  sedimentation  basins  may  be  omitted  entirely. 

After  passing  through  the  basins  the  water  is  collected  by  the 
inlets  of  the  pipe  manifold  at  the  lower  end,  which  is  connected 
with  the  settled  water  main  extending  through  the  court  between 
the  two  rows  of  filters.  Branches  from  this  main  lead  to  each 
filter,  terminating  within  the  filter  in  a  float  valve  which  maintains 
a  uniform  depth  of  water  over  the  sand. 

Each  filter  consists  of  a  water-tight  basin  of  masonry  or  rein- 
forced concrete,  generally  roofed  over  with  a  groined  arch  con- 
struction supported  on  columns,  the  whole  being  covered  with 
several  feet  of  soil  and  sodded,  as  an  additional  protection  against 
freezing  of  the  water,  which  materially  affects  the  efficiency  of 


TYPES    OF    PURIFICATION    PLANTS 


23 


24  WATER   PURIFICATION   PLANTS 

filtration.  Covering  the  filter  also  prevents  the  formation  of 
algae,  by  excluding  the  light  necessary  for  their  growth.  Access 
to  the  interior  is  provided  by  an  inclined  runway  and  by  numerous 
double-covered  manholes  in  the  roof,  which  also  furnish  the 
necessary  light  and  ventilation  for  carrying  on  work  in  the  filter. 
The  area  of  these  filter  units  is  from  one-fourth  to  one  acre  or  more, 
depending  on  the  total  capacity  of  the  plant. 

The  filtering  medium  consists  of  a  bed  of  clean  quartz  sand  h, 
of  a  size  of  grain  approximating  that  of  granulated  sugar.  In 
technical  terms  it  has  an  effective  size  *  of  about  0.3  to  0.4  milli- 
meters and  a  uniformity^  coefficient  of  about  1.5.  The  depth  of 
sand  bed  is  generally  from  3  to  4  feet  in  a  new  filter,  decreasing  as 
the  dirty  sand  is  scraped  off  with  continued  use.  This  sand  is 
underlain  with  a  foot  of  gravel  i,  so  graded  as  to  increase  in  coarse- 
ness toward  the  bottom.  The  function  of  this  gravel  is  to  prevent 
the  sand  from  being  washed  into  the  collector  system  with  the 
filtered  water,  and  to  allow  ample  water  passages  through  which 
the  filtrate  can  flow  to  the  collecting  pipes.  Open-jointed  tile 
pipes  j,  from  4  to  8  inches  in  size,  rest  on  the  filter  bottom,  buried 
in  and  surrounded  by  the  gravel.  Generally  one  such  collector 
pipe  serves  the  area  between  two  adjacent  rows  of  columns,  and 
carries  the  filtered  water  to  the  main  collector  fc,  which  is  placed 
through  the  center  of  the  filter  unit. 

It  is  most  important  that  the  filtration  proceed  at  a  uniform 
rate.,  and  to  this  end  each  filter  unit  is  provided  with  a  regulator 
house  I,  the  lower  portion  of  which  forms  a  water-tight  well  con- 
taining the  regulation  mechanism.  The  arrangement  shown,  used 
in  the  Albany  plant  by  Mr.  Allen  Hazen,  will  illustrate  the  general 
principle  of  regulation,  although  not  of  the  most  recent  type.  It 
does  not  profess  to  operate  automatically,  and  therefore  will  better 
serve  to  emphasize  the  attention  required  to  maintain  a  uniform 
rate  of  filtration,  even  by  more  recent  "  automatic  "  types.  The 
well  is  divided  into  two  parts  by  a  concrete  diaphragm  m,  and  by 
tight  wooden  stop  planks  above  the  diaphragm.  The  filtrate, 
collected  by  the  main  k,  flows  into  the  first  compartment  of  the 
well  through  the  valve  o,  rising  therein  to  a  height  lower  than  the 

*  The  effective  size  of  a  sand  is  that  size  of  sand  grain  than  which  90  per 
cent  of  the  grains  are  larger. 

t  The  uniformity  coefficient  is  the  ratio  of  the  size  of  sand  grain  than  which 
60  per  cent  is  finer,  to  the  effective  size. 


TYPES   OF    PURIFICATION   PLANTS  25 

water  level  over  the  sand  by  a  distance  r,  representing  the  friction 
of  the  water  through  the  sand,  gravel,  and  under-drain  system  or 
"  loss  of  head  "  through  the  filter.  The  water  flows  through  the 
orifice  n  into  the  second  compartment  of  the  well,  and  thence 
through  a  valved  branch  pipe  to  the  main  s,  which  carries  the 
effluent  of  all  the  units  to  the  filtered  or  "  clear  "  water  basin, 
ready  for  delivery  into  the  distribution  system.  The  rate  of  flow 
through  the  orifice  n  is  a  function  of  the  difference  in  water  level 
between  the  two  compartments  of  the  well  when  the  orifice  is 
submerged,  and  a  function  of  the  water  level  in  the  first  compart- 
ment when  that  in  the  second  is  below  the  bottom  of  the  orifice. 
By  arranging  a  float  in  each  compartment  so  as  to  indicate  this 
difference  in  water  level  on  a  dial,  the  rate  of  filtration  may  be 
determined  from  the  reading  of  the  dial,  and  can  be  regulated  to 
the  desired  amount  by  means  of  the  graduated  valve  o.  Two 
other  floats,  similarly  arranged,  indicate  the  loss  of  head  through 
the  filter.  A  valve  and  drain  pipe  are  provided,  leading  to  a 
main  drain  for  emptying  the  filter. 

Rate  and  Loss  of  Head.  The  rate  of  filtration  varies  from 
2,000,000  to  6,000,000  gallons  per  acre  per  day,  3,000,000 
gallons  being  very  commonly  used.  The  rate  used  at  any  plant 
should  be  varied  as  experience  dictates,  the  controlling  elements 
being  the  quality  of  effluent,  which  will  deteriorate  with  too  high 
rates,  and  the  period  between  cleaning  the  filters,  which  will 
shorten  under  the  same  conditions,  and  may  become  so  frequent 
as  to  prove  uneconomical.  The  head  of  water  required  to  force 
the  water  through  the  filter  at  the  determined  rate  is  measured  by 
the  loss-of-head  gage.  For  any  given  rate  of  filtration  the  loss 
of  head  increases  with  the  length  of  time  the  filter  is  in  operation, 
due  to  the  deposits  of  silt  formed  on  and  in  the  filter  sand,  which 
greatly  augment  the  friction  through  same,  until  finally  the  head  of 
water  would  become  sufficient  to  break  down  the  resistance  of  the 
sand,  causing  unfiltered  water  to  find  its  way  into  the  collector 
mams.  At  a  safe  interval  before  this  occurs,  the  filter  must  be 
shut  down  and  either  raked  or  cleaned  by  scraping.  This  maxi- 
mum loss  of  head  may  be  conservatively  placed  at  from  5  to  6 
feet.  The  required  head  should  be  furnished  by  the  water  above 
the  sand,  that  is,  the  water  level  in  the  first  compartment  of  the 
regulator  well  should  never  fall  below  the  level  of  the  top  of  the 
sand.  Should  this  occur,  a  "  negative  head  "  or  partial  vacuum 


26  WATER  PURIFICATION   PLANTS 

will  form  in  the  upper  portion  of  the  sand  bed,  resulting  in  the 
liberation  of  some  of  the  dissolved  air  from  the  water,  thereby 
causing  disturbances  in  the  filtering  process.  This  is  especially 
prone  to  happen  in  cold  weather,  as  the  dissolved  air  carried  by  the 
water  is  then  at  a  maximum. 

The  Theory  of  Filtration.  Filtration  is  a  combination  of 
several  processes.  The  most  obvious  of  these,  although  not  the 
most  important,  is  the  straining  out  of  particles  too  large  to  pass 
the  interstices  between  the  sand  grains.  However,  as  most  of  the 
particles  of  suspended  matter  are  so  small  as  to  readily  pass 
through  these  spaces,  it  is  obvious  that  other  processes  must  be 
acting  to  remove  them  from  the  water.  The  small  pockets  formed 
by  adjacent  sand  grains  act  as  minute  sedimentation  basins  in 
which  the  suspended  matter  may  settle.  Bacterial  action  plays 
a  most  important  role.  After  a  filter  is  in  operation  for  a  time  a 
slimy  gelatinous  film  forms  on  the  surface  and  explorations  into 
the  sand  will  show  similar  jelly-like  matter  forming  between  or 
coating  the  sand  grains.  Examination  will  show  this  jelly  to  be 
of  bacterial  origin,  as  is  also  shown  by  the  fact  that  it  forms  when 
filtering  clear  waters.  The  surface  coating  has  been  named  the 
Schmutzdecke  (dirt  cover)  by  the  Germans,  who  attribute 
most  of  the  efficacy  of  the  filter  to  its  action,  and  place  so  much 
confidence  in  it  that  they  consider  a  sand  bed  a  foot  thick  sufficient, 
if  properly  coated,  to  yield  a  satisfactory  effluent.  The  Schmutz- 
decke probably  retards  much  of  the  suspended  and  colloidal  matter, 
but  the  bacterial  jelly  within  the  sand  is  also  important  both  be- 
cause of  its  straining  effect  and  because  it  entraps  and  holds 
particles  of  silt  and  bacteria  on  the  "  sticky-fly-paper  "  principle. 
The  efficiency  of  a  filter  increases  with  age,  due  to  continued  bac- 
terial growth  and  the  resulting  formation  of  slime  and  jelly  in  the 
interior.  This  jelly-like  matter  is  capable  of  absorbing  color 
from  the  raw  water  and  may  effect  a  reduction  up  to  25  per  cent. 
There  is  also  a  small  amount  of  chemical  action  within  the  filter, 
in  the  way  of  oxidation  of  the  dissolved  organic  matter  contained 
in  the  water. 

While  a  properly  working  filter  bars  the  passage  of  practically 
all  the  bacteria  in  the  raw  water,  a  considerable  number  may 
sometimes  be  found  in  the  effluent.  It  has  been  proven  by  experi- 
ment that  these  result  from  growths  in  the  sand  and  under  drains, 
and  also  that  they  are  harmless  varieties. 


TYPES    OF    PURIFICATION    PLANTS 


27 


28  WATER   PURIFICATION   PLANTS 

Raking  the  Filters.  When  the  loss  of  head"  becomes  excessive, 
due  to  clogging  of  the  filter  sand,  conditions  may  be  relieved  by 
loosening  the  surface  by  means  of  ordinary  rakes.  It  is  found  that, 
after  raking,  the  filter  clogs  more  rapidly  than  before,  so  that  re- 
peated raking  more  than  twice  in  succession  is  impracticable 
and  scraping  must  be  resorted  to. 

Scraping  the  Filters.  In  the  lower  left  corner  of  Fig.  4  a  filter 
is  shown,  as  it  would  appear  with  the  roof  removed,  undergoing 
the  process  of  cleaning  by  scraping.  The  filter  is  shut  down  and 
drained,  and  the  surface  of  the  sand  is  removed  to  a  depth  of  one- 
half  to  one  inch  with  broad  flat  shovels,  and  gathered  into  con- 
venient piles.  The  piles  of  dirty  sand  are  removed  by  means  of  a 
portable  sand  ejector  t,  shown  in  detail  by  Fig.  5.*  This  consists 
of  a  tight  metal  box  containing  a  large  ejector,  operating  under 
water  pressure  furnished  by  a  three  or  four  inch  pipe.  The  sand 
is  shoveled  into  this  box,  where  it  is  kept  in  a  fluid  condition  by 
water  jets  from  several  perforated  "  irrigating  pipes  "  in  the 
bottom  of  the  box.  In  this  fluid  or  suspended  condition  it  is 
drawn  into  the  ejector  and  discharged  through  a  "  sand  pipe  " 
(generally  4  inches  in  diameter)  leading  to  the  sand  washers  u-u. 
Pressure  and  sand  pipes  are  located,  with  convenient  outlets,  along 
the  filter  walls,  so  that  the  ejector  can  be  attached  at  any  desired 
point  by  means  of  hose  connections.  The  sand  washer  is  shown  in 
detail  by  Fig.  6.f  It  consists  of  a  conical  metal  hopper,  in  the 
throat  of  which  are  located  an  ejector  and  an  auxiliary  jet,  the  pur- 
pose of  which  is  to  supply  sufficient  water  to  maintain  a  con- 
tinual upward  current  which  escapes  by  means  of  the  overflow 
notch  at  the  top  of  the  hopper.  The  mixture  of  dirty  sand  and 
water  from  the  filter  enters  the  hopper  from  above  and  settles 
toward  the  bottom  against  the  continual  upward  current  from 
the  auxiliary  jet.  The  dirt  and  silt  are  thus  removed  and  carried 
up  and  out  of  the  hopper  via  the  overflow.  The  sand  settles  to  the 
bottom,  where  it  is  seized  by  the  ejector  and  carried  through 
piping  to  the  sand  storage  bins  x-x.  Two  washers  are  generally 
operated  in  series,  washing  the  sand  twice,  and  the  dirty  overflow 
water  passes  through  several  concrete  boxes  w  on  its  way  to  the 
sewer,  so  that  any  fine  sand  carried  over  may  be  trapped  therein, 

*  Trans.  Am.  Soc.  C.  E.,  1904,  1.  Ill,  p.  227. 
t  Trans.  Am.  Soc.  C.  E.,  1906,  1.  VII,  p.  586. 


TYPES    OF    PURIFICATION    PLANTS 


29 


30  WATER   PURIFICATION    PLANTS 

preventing  the  clogging  of  the  sewer.  The  sand  bins  x-x  have 
conical  bottoms  provided  with  drains,  so  that  the  water  may  be 
removed  from  the  sand. 

In  winter  it  is  difficult  to  wash  sand,  owing  to  trouble  with 
freezing  pipes,  ice,  etc.,  and  it  is  therefore  customary  to  scrape  the 
sand  into  piles,  to  await  the  advent  of  warmer  weather  for  washing. 
If  these  piles  tend  to  grow  so  large  as  to  seriously  cut  down  the 
effective  area  of  the  filter,  open-bottomed  boxes  or  frames  are 
placed  in  the  filter  and  the  sand  shoveled  into  these,  being  thereby 
more  closely  confined. 

The  frequency  of  scraping  is  a  factor  of  the  turbidity  of  the 
settled  water  and  the  rate  of  filtration.  In  the  worst  cases  it  may 
be  required  at  intervals  of  a  few  days;  under  favorable  conditions 
the  period  between  scrapings  may  be  from  four  to  six  weeks.  The 
advantage  of  preliminary  sedimentation  in  this  connection  is 
obvious. 

After  scraping,  the  sand  surface  is  smoothed  and  the  filter  is 
slowly  filled  with  purified  water  from  below,  and  when  this  has  risen 
well  above  the  sand,  raw  water  is  introduced  and  filtration  slowly 
started,  with  frequent  examinations  as  to  the  quality  of  the 
effluent. 

Replacing  Sand.  When,  by  several  scrapings,  about  a  foot  of 
sand  has  been  removed,  the  filter  is  resanded  to  its  original  level. 
To  do  this,  it  is  first  scraped  to  a  greater  depth  than  usual,  to  make 
sure  of  removing  all  the  dirty  sand,  and  is  then  filled  with  water 
to  the  level  at  which  it  is  desired  the  sand  surface  should  come. 
Ejectors  placed  in  the  sand  bins  discharge  clean  sand  through 
sand  return  pipes  terminating  in  lines  of  hose  which  are  floated  on 
small  rafts  over  the  surface  of  the  filter  to  be  resanded,  and  which 
are  guided  so  as  to  distribute  the  sand  evenly.  When  the  desired 
level  is  reached,  the  water  is  drawn  down,  the  surface  smoothed 
over,  and  the  filter  started. 

General  Operation.  The  general  remarks  on  operation  given 
hereafter  apply  to  slow  sand  as  well  as  to  rapid  sand  filtration.  If 
coagulants  are  used,  the  tests  and  methods  given  apply;  if  not,  the 
chemical  tests,  in  the  main,  may  be  omitted,  and  much  stress 
placed  on  the  bacterial  tests.  The  interpretation  of  tests  as  re- 
gards bacteria  and  coli  holds  also.  Much  attention  should  be 
given  to  bacterial  tests  of  the  effluents  of  individual  filters. 

Sterilization.     It  has  become  customary  of  late  ye'ars  to  treat 


TYPES   OF   PURIFICATION   PLANTS  31 

the  filtrate  with  hypochlorite  of  lime,  as  an  additional  precaution. 
This  is  explained  in  detail  in  Chapter  VI.  Needless  to  say,  the 
hypochlorite  cannot  in  this  case  be  applied  to  the  settled  water, 
as  this  would  interfere  with  the  bacterial  action  within  the  filter. 

Modern  Tendencies  in  Slow  Sand  Filtration.  There  is  a 
tendency  toward  increased  rates  of  filtration,  in  the  most  recent 
plant  6,000,000  gallons  per  acre  per  day  being  used.  With  turbid 
waters  adequate  coagulation  and  sedimentation  have  been  intro- 
duced, as  an  adjunct  to  higher  rates,  and  to  relieve  the  filters  of 
part  of  the  load.  Extensive  experiments  have  been  made  with 
apparatus  for  washing  the  sand  in  place,  but  as  yet  have  not  been 
entirely  successful.  Centralization  of  control  by  leading  all 
piping  to  one  common  regulator  house  has  also  been  attempted. 
It  will  be  seen  that  all  these  improvements  tend  toward  a  quasi- 
mechanical  type  of  filtration. 

Mechanical  Filtration.  The  primary  difference  between  rapid 
or  mechanical  and  slow  sand  filtration  is  in  the  higher  rate  used  in 
the  former  process— 100  to  150,000,000  as  against  3,000,000  gallons 
per  acre  per  day,  or  about  50  to  1.  This  high  rate  necessitates 
relieving  the  filters  of  the  burden  of  removing  coarse  suspended 
matter,  which  is  accomplished  by  coagulation  and  sedimentation. 
It  also  follows  that,  as  the  rate  of  clogging  the  sand  varies  directly 
with  the  rate  of  filtration,  the  filter  beds  must  be  cleaned  daily,  and 
of  necessity  this  must  be  done  in  situ,  to  avoid  a  laborious  removal 
and  replacing  of  the  sand.  Since  there  is  no  time  for  the  forma- 
tion of  a  Schmutzdecke  by  natural  biological  processes,  a  substitute 
must  be  supplied  in  the  shape  of  a  jelly-like  film,  or  "  mat,"  of 
coagulum,  which  forms  with  great  rapidity  on  starting  the  filter 
after  cleaning. 

Description  of  Plant.  Fig.  7  shows  a  typical  rapid  sand 
filtration  plant.  The  general  similarity,  in  parts  and  arrangement, 
to  the  slow  sand  plant  is  readily  grasped.  The  most  striking  feature 
is  the  contraction  or  concentration  of  the  whole  plant  as  compared 
with  the  slow  sand  type.  The  settling  basin  is  present  as  before, 
but  is  often  deeper  and  of  a  different  type  of  construction  and  more 
thoroughly  baffled.  The  office  and  laboratory  building  remains, 
containing  also  the  coagulant  apparatus  and  storage,  for  which 
reason  it  is  frequently  called  the  "  coagulant  house  or  building." 
The  court  between  the  filters  assumes  a  different  shape,  though 
maintaining  its  functions,  by  being  divided  into  a  lower  story  or 


32 


WATER    PURIFICATION    PLANTS 


TYPES   OF   PURIFICATION   PLANTS  33 

pipe  gallery,  containing  the  piping,  valves,  and  regulating  devices, 
and  an  upper  operating  platform.  We  may  imagine  the  individual 
regulator  houses  as  expanding  and  merging  into  one  continuous 
structure  over  both  the  former  court  and  the  greatly  contracted 
filter  units,  their  former  locations  being  indicated  only  by  the  re- 
maining characteristic  groups  of  valve  stands  on  the  operating 
platform. 

The  advantages  of  this  new  arrangement  as  regards  ease  of 
operation  and  access  to  all  parts  are  easily  seen.  The  whole 
filtering  area  is  under  the  eye  of  the  operator;  he  may  examine  the 
distribution  of  the  raw  water  and  its  quality  at  all  points.  By 
manipulating  a  few  valves,  he  may  drain  any  unit  sufficiently  to 
examine  the  sand  surface  and  mat,  in  a  very  short  time.  The 
tendency  toward  vertical  stratification  of  the  sand  is  nullified  by 
the  small  area,  and  a  uniform  horizontal  hydraulic  grading  of  the 
sand  bed  is  maintained  by  frequent  washing.  The  capacity  of  the 
units  is  generally  less  than  those  used  in  slow  sand  filtration,  so  that 
the  effluent  may  be  more  closely  controlled  by  individual  samples, 
and  any  defective  unit  can  be  shut  down  immediately,  with  small 
loss  of  pumped  and  coagulated  water,  and  the  fault  can  be  found 
and  corrected  with  a  minimum  of  labor.  The  formation  of  the 
mat,  or  artificial  Schmutzdecke,  can.be  controlled  as  to  consistency 
and  thickness  by  applying  coagulants  directly  to  the  raw  water  in 
the  filter  after  washing. 

Two  important  differences  in  the  theory  and  operation  are 
these :  bacterial  growths  in  the  filter  bed  are  not  required,  owing  to 
the  artificial  mat  formation;  therefore  the  beds  may  be  sterilized 
by  adding  hypochlorite  to  the  settled  water,  and  the  presence  of 
"after-growth  "  bacteria  in  the  effluent  done  away  with.  Negative 
head  in  the  sand  bed,  so  scrupulously  avoided  in  slow  sand  filtra- 
tion, is  featured  in  the  rapid  process,  as  decreasing  the  necessary 
depth  of  filter  tubs  and  tending  toward  a  uniform  distribution  of 
rate  over  the  bed.  This  is  possible  because  the  filters  are  washed 
so  frequently  as  to  minimize  the  chance  of  sufficient  air  being 
liberated  within  the  bed  to  affect  the  operation. 

Settling  Basins.  The  settling  basin  shown  in  Fig.  7  is  con- 
structed of  reinforced  concrete,  of  a  type  frequently  adopted  where 
land  is  limited  or  expensive,  as  the  vertical  side  walls  give  a  maxi- 
mum capacity  with  the  least  area.  A  basin  similar  to  that  shown 
in  Fig.  4  with  earth  embankments  is  less  frequently  used  for  me- 


34  WATER   PURIFICATION   PLANTS 

chanical  filter  plants.  The  water  enters  through  the  inlet  manifold, 
terminating  in  the  risers  b-b-b-b,  which  may  extend  above  the 
water,  acting  as  aerators  as  shown,  or  not,  according  to  the  condi- 
tions to  be  met.  The  basin  is  provided  with  baffles,  Ci-C2-C3, 
whose  function  it  is  to  prevent  undercurrents  and  to  maintain 
a  uniform  flow  throughout  the  basin.  After  passing  through 
the  basin  the  water  is  collected  by  the  risers  d-d-d-d  of  the  outlet 
manifold  and  carried  to  the  filters  through  the  settled  water 
main  e. 

The  floor  of  the  basin  is  of  smooth  concrete  with  a  decided  pitch 
from  all  sides  toward  the  center,  where  a  sump  /  is  located.  In 
this  sump  is  a  drain  valve  operated  by  a  handwheel  h,  by  means  of 
which  the  basin  may  be  emptied  for  cleaning  through  the  drain  g. 
After  being  emptied,  the  remaining  mud  is  washed  out  through  the 
drain  by  means  of  a  hose.  Fig.  7  shows  a  single  basin,  which 
necessitates  either  shutting  down  while  cleaning,  or  by-passing  the 
water  directly  to  the  filters  by  closing  valves  i  and  j  and  opening 
valve  k.  Many  plants  have  duplicate  basins,  one  of  which  may  be 
cleaned  at  a  time  without  interference  with  the  operation  of  the 
plant. 

Coagulating  Apparatus.  The  coagulant  house  shown  is  three 
stories  high.  The  first  floor  forms  the  main  entrance  to  the  filter 
house,  contains  the  wash  water  pumps,  air  compressor,  receiving 
room  and  storage  for  coagulants,  stairway  to  upper  floors,  etc. 
The  second  floor  contains  the  combined  office  and  laboratory,  the 
solution  tanks  l-l-l  and  orifice  boxes  m-m-m,  from  which  pipes 
n-n-n  carry  the  coagulant  solution  and  discharge  it  into  the  raw 
water  main  a  at  o.  Sometimes  additional  coagulant  pipes  are 
provided,  so  that  the  coagulants  may  be  introduced  at  the  center 
baffle  of  the  settling  basin,  C2,  or  into  the  settled  water  main  e. 
The  third  floor  is  on  a  level  with  the  tops  of  the  solution  tanks  and 
is  used  for  charging  these  and  for  coagulant  storage.  It  also  con- 
tains a  scale  for  weighing  chemicals  and  the  stirring  apparatus  of 
the  tanks.  An  elevator  or  hoist  is  installed,  serving  all  floors,  but 
primarily  for  carrying  up  barrels  and  sacks  of  coagulant  to  the 
third  floor. 

Fig.  8  shows  in  section  a  typical  solution  tank  and  orifice  box. 
Except  when  used  for  lime,  these  tanks  are  generally  built  of  re-, 
inforced  concrete.  On  top  of  the  tank  is  a  dissolving  box  with  a 
perforated  bottom,  into  which  the  weighed  coagulant  is  dumped 


TYPES    OF    PURIFICATION    PLANTS 


35 


Depth  Gage 


Water  Motor 


To  Raw  Water 


FIG.  8. — Section  of  a  Coagulant  Tank  and  Orifice  Box. 


36  WATER    PURIFICATION    PLANTS 

and  dissolved  by  a  spray  of  hot  water,  the  solution  flowing  through 
the  perforations  into  the  tank.  An  automatic  float  shuts  off  the 
hot  water  when  the  tank  is  full,  to  prevent  overflowing.  Before 
starting  to  use  the  solution  the  operator  closes  the  hot-water 
valve  by  hand.  In  the  tank  are  mixing  paddles  attached  to  a 
vertical  shaft,  rotated  by  bevel  gearing,  belt-driven  from  a  water 
or  electric  motor.  These  paddles  keep  the  solution  thoroughly 
mixed  and  of  uniform  strength  throughout. 

From  the  bottom  of  the  tank,  a  short  valved  pipe  connection 
leads  to  the  orifice  box.  It  is  the  function  of  this  device  to  feed  the 
solution  into  the  coagulant  pipe  at  a  constant  rate,  regardless  of  the 
amount  in  the  solution  tank.  To  this  end  a  float  valve  on  the  inlet 
maintains  a  constant  head  on  an  orifice  or  opening  in  a  thin 
metal  plate  in  the  bottom  of  the  box,  under  which  conditions,  by 
the  laws  of  hydraulics,  the  flow  through  the  orifice  will  be  constant 
and  proportional  to  its  area  of  opening.  A  sliding  or  rotating  disk 
allows  this  area,  and  consequently  the  rate,  to  be  varied,  and  a 
graduated  handwheel  is  provided,  so  that  the  size  of  opening  may 
be  known  to  the  operator.  A  screen  across  the  box  prevents 
large  particles  from  obstructing  the  orifice,  and  the  glass  front 
allows  the  operator  a  view  of  the  interior,  and,  by  a  mark  etched 
upon  it,  tells  him  at  a  glance  whether  the  water  in  the  box  is  at  the 
correct  level,  a  most  important  point,  as  the  rate  of  flow  varies 
with  the  water  level  over  the  orifice.  This  is  but  one  of  a  very 
diverse  variety  of  orifice  boxes,  which  differ  in  detail,  but  not  in 
principle.  Some  are  arranged  to  automatically  vary  the  orifice 
opening  with  variations  in  the  rate  of  the  raw  water,  a  desirable 
point  if  it  does  not  lead  to  neglect  by  the  operator,  for  automatic 
devices  act  as  such  only  when  given  the  necessary  attention,  which 
is  increased  over  that  required  by  simple  non-automatic,  in  pro- 
portion to  their  degree  of  complexity. 

The  solution  tank  should  be  provided  with  a  float  gage  for 
indicating  the  depth  of  solution  and  having  in  conjunction  a  low- 
water  alarm,  consisting  of  an  electric  bell  which  will  ring  when  the 
solution  tank  is  about  to  become  empty.  The  dial  of  the  float 
gage  is  conveniently  graduated  as  in  Fig.  9,  where  it  is  seen  that, 
besides  the  depth  scale,  concentric  scales  are  added  corresponding 
to  the  opening  of  the  orifice  box,  these  being  graduated  in  hours, 
so  that  in  charging  the  tank,  knowing  the  opening  of  the  orifice  box 
and  length  of  run,  the  operator  can  fill  the  tank  to  the  required 


TYPES    OF    PURIFICATION    PLANTS 


37 


FIG.  9.— Dial  for  a  Solution  Tank  Depth  Gage. 


FIG.  10. — Dissolving  Device  for  Hypochlorite  of  Lime. 


38 


WATER    PURIFICATION    PLANTS 


TYPES   OF   PURIFICATION   PLANTS  39 

depth,  or  if  the  opening  of  the  orifice  is  changed  during  a  run,  he 
can  tell  at  a  glance  how  long  the  tank  will  last  at  the  new  rate. 

Each  solution  tank  is  provided  with  a  drain  and  valve  for  clean- 
ing purposes. 

Lime  cannot  be  dissolved  directly  in  the  manner  described, 
but  before  being  poured  into  the  solution  tank  must  be  slaked,  as 
described  in  Chapter  IX.  This  requires  the  use  of  iron  slaking 
boxes. 

Hypochlorite  of  lime  presents  some  difficulties  owing  to  its 
comparative  insolubility  and  its  lightness,  causing  it  to  float  on  the 
water  like  flour.  The  home-made  device  shown  in  Fig.  10  is  very 
handy  for  dissolving  hypo  in  small  plants.  It  consists  of  an  ice- 
cream freezer,  with  the  can  perforated  with  numerous  small  holes 
(say  one-eighth  inch) .  The  freezer  pail  is  bolted  solidly  to  the  top 
of  the  solution  tank.  A  valved  drain  is  provided  from  the  freezer 
to  the  tank,  as  well  as  a  supply  of  warm  water  to  keep  the  pail 
filled.  The  weighed  hypo  is  placed  in  the  perforated  can,  and  the 
pail  filled  with  water.  On  turning  the  freezer  the  paddles  force 
the  hypo  toward  the  periphery  of  the  can  by  centrifugal  force,  and 
the  scrapers  squeeze  it  through  the  perforations  in  the  can.  The 
freezer  should  be  large  compared  to  the  amount  of  hypo  used,  and 
all  possible  parts  should  be  well  coated  with  asphalt  paint,  to 
prevent  corrosion. 

Fig.  11  shows  a  hypochlorite  plant  suitable  for  treating  the 
unfiltered  water  supply  of  a  city.  It  consists  of  dissolving  ap- 
paratus, two  orifice  boxes,  two  solution  tanks,  stirring  devices, 
hypo  storage,  and  laboratory.  To  dissolve  the  hypo,  which  is 
received  in  sheet-metal  canisters,  a  canister  is  suspended  from 
the  traveling  scale  and  run  over  the  dissolving  box.  The  at- 
tendant cuts  two  holes  in  the  end  of  the  canister,  one  at  the  top 
and  one  at  the  bottom.  By  directing  a  stream  of  water  under 
pressure  into  the  upper  hole,  the  hypo  is  washed  out  through  the 
lower  hole  into  the  dissolving  box.  Thence  it  flows  into  one  of  the 
solution  storage  tanks  and  passes  through  the  orifice  box  into  the 
water.  In  dissolving  the  hypo,  the  attendant  wears  a  mask  and 
goggles  and  receives  fresh  air  under  slight  pressure  through  a 
hose.  Thus  annoyance  from  fumes  and  dust  are  obviated.  A 
similarly  designed  apparatus  can  be  used  in  connection  with 
filtration  plants. 

The  Filters.     Figs.  12  and  13  show  respectively  the  part  plan 


40  WATER   PURIFICATION   PLANTS 

and  section  of  a  modern  concrete  filter  house.  Referring  to  Fig. 
13,  it  will  be  seen  that  the  niters  are  in  two  rows,  with  the  pipe 
gallery  and  operating  platform  between  them,  and  a  subbasement 
for  filtered  water  storage  below,  making  a  very  compact  and  eco- 
nomical arrangement.  The  water  from  the  settling  basin  enters  the 
pipe  gallery  through  the  settled  water  main  e,  extending  the  length 
of  the  gallery  with  a  valved  branch  to  each  filter.  The  level  of  the 
water  on  the  filters  may  be  regulated  by  float  valves  attached  to 
the  ends  of  the  settled  water  inlets,  as  shown  in  the  right-hand 
filter  of  Fig.  13,  or  the  level  for  all  the  filters  may  be  fixed  by  an 
overflow  pipe  in  the  settling  basins. 

The  nature  of  the  filtering  material  through  which  the  water 
passes  is  shown  in  the  section,  Fig.  13.  It  consists  of  a  30-inch 
layer  of  sand  similar  to  that  used  in  slow  sand  filters  in  quality,  but 
slightly  coarser  (effective  size  0.4  to  0.6  mm.).  In  operation  it  is 
covered  with  a  mat  or  film  of  coagulum.  The  sand  rests  on  about 
a  foot  of  graded  gravel,  generally  increasing  in  size  from  one- 
eighth  inch  at  the  top  to  three-quarters  inch  at  the  bottom.  The 
gravel  in  turn  is  supported  by  perforated  brass  strainers,  through 
which  the  water  passes  to  the  collector  pipes  below.  Fig.  14 
shows  several  types  of  strainer  systems.  The  upper  type  is  ex- 
tensively used  in  plants  using  a  high  rate  of  wash.  The  bottom  of 
the  filter  is  molded  into  a  series  of  parallel  ridges  and  grooves,  ap- 
proximately of  the  dimensions  shown,  all  leading  to  a  central 
collecting  gutter.  The  grooves  or  valleys  have  ledges  on  which 
rest  perforated  brass  plates  supporting  the  gravel.  The  portion 
of  the  groove  below  the  strainer  plate  serves  as  a  collecting  channel 
for  the  filtered  water.  The  gravel  is  confined  between  the  ridges 
and  is  held  down  against  the  upward  pressure  while  washing  by  a 
brass  wire  screen.  A  somewhat  similar  strainer  system  is  in  use 
at  the  Columbus,  Ohio,  plant  and  is  shown  by  Fig.  42.  The  lower 
types  are  in  general  use  at  plants  where  both  air  and  water  are 
used  in  washing,  and  are  similar  to  that  shown  in  Fig.  13.  There 
is  a  main  collector  through  the  center  of  the  filter  with  lateral 
pipes  (generally  2-inch  diameter  and  spaced  six  inches  on  centers) . 
Into  these  lateral  pipes  brass  strainers  are  screwed.  The  left-hand 
side  of  the  cut  shows  the  arrangement  for  separate  air  and  wash- 
water  manifolds.  In  this  case  the  perforated  brass  air  laterals  are 
placed  just  above  the  gravel.  The  strainer  heads  shown  are  of  the 
slotted  type,  the  wash  water  being  distributed  laterally  through 


TYPES    OF    PURIFICATION    PLANTS 


41 


FIG.  12.— Plan  of  a  Small  Filter  Building,  Showing  Filter  Units  and  Piping. 


42 


WATER    PURIFICATION    PLANTS 


TYPES   OF  PURIFICATION   PLANTS 


43 


the  slots.  The  right-hand  strainers  are  of  the  patented  combined 
air  and  wash-water  type  (Williamson  strainers).  It  will  be  noted 
that  the  strainer  shanks  extend  almost  to  the  bottom  of  the 
lateral  pipes.  To  wash  with  air,  the  air  is  admitted  to  the  upper 
half  of  the  lateral  pipes,  which  contain  sufficient  water  to  seal  the 


Perforated  Brass  Plate 
64%,  in.  holes  per  lin.ft. 


.  Combined 
/Air  and  Wash 

FIG.  14. — Typical  Strainer  Systems  Used  in  Mechanical  Filters. 

extended  ends  of  the  strainer  shanks.  The  air  escapes  through 
the  strainers  via  small  holes  drilled  in  the  shanks  of  the  strain- 
ers. There  are  many  types  of  strainers  in  use  other  than  those 
described. 

As  in  the  case  of  slow  sand  filters,  the  laterals  discharge  into  a 
main  collector,  bisecting  the  filter,  which  carries  the  filtered  water 
to  an  effluent  or  rate  controller,  situated  in  the  pipe  gallery,  one 
being  provided  for  each  filter  unit.  Owing  to  the  rapid  increase  in 
loss  of  head,  automatic  control  is  here  imperative.  If  the  filters 


44 


WATER   PURIFICATION   PLANTS 


operate  under  negative  head,  the  controllers  are  set  some  distance 
below  the  niters,  which  requires  them  to  regulate  equally  well 
with  their  outlets  under  back  pressure  from  the  clear-water  basin. 


FIG.  15.— Rate  of  Flow  Controller  for  Mechanical  Filters.    Orifice  Box  Type. 

It  is  also  desirable  that  they  should  operate  with  a  minimum  dif- 
ference of  head.     The  conditions  practically  eliminate  the  fixed- 


FIG.  16. — Rate  of  Flow  Controller  for  Mechanical  Filters.    Velocity  Type. 

head-over-orifice  type,  Fig.  15  (such  as  described  for  the  slow  sand 
plant,  or  an  enlarged  orifice  box) ,  and  require  a  device  wherein  the 
velocity  head  or  an  artificially  created  difference  of  head  in  the 


TYPES    OF   PURIFICATION    PLANTS 


45 


effluent  pipe  regulates  the  area  of  a  valve  pro  rata.     A  typical  con- 
troller of  the  velocity  type  is  shown  diagrammatically  in  Fig.  16.* 


FIG.  17. — Rate  of  Flow  Controller  for  Mechanical  Filters.    Venturi  Type. 


Courtesy  Simplex  Valve  and  Meter  Company. 

FIG.  17a.— Venturi  Type  Rate  Controller. 

The  water  flows  downward  through  the  draft  tube  a  and  striking 
the  plate  b  has  its  direction  reversed  so  that  it  impinges  on  the 
inverted  hollow  cylinder  c,  the  sides  of  which  form  the  gates  over 

*  Made  by  the  Norwood  Engineering  Co.  for  the  Charleroi,  Pa.,  plant. 


46  WATER    PURIFICATION    PLANTS 

the  apertures  d-d-d.  The  impact  of  the  water  raises  the  cylinder 
in  proportion  to  the  velocity  in  the  draft  tube,  thereby  throttling 
the  apertures  d-d-d,  and  allowing  the  water  to  escape  as  indicated 
by  arrows.  By  means  of  a  cone  valve  e  regulated  from  a  valve 
stand  on  the  operating  floor,  the  controller  can  be  set  to  any  de- 
sired rate.  Fig.  17  is  a  schematic  sketch  of  a  controller  of  the  dif- 
ference-in-head  type.  An  obstruction,  such  as  a  Venturi  tube, 
orifice  plate,  etc.,  is  placed  in  the  effluent  pipe  at  a,  followed  by  a 
valve  b  whose  opening  is  regulated  by  the  position  of  the  piston  c. 
The  position  of  this  piston  is  determined  by  the  difference  between 
the  direct  upward  pressure  from  below  the  obstruction  and  the 
downward  pressure  transmitted  to  the  top  of  the  piston  from  above 
the  obstruction  by  means  of  the  pipe  d.  The  controller  can  be 
set  to  deliver  at  any  desired  rate  by  the  position  of  the  weight  w 
on  the  lever  arm. 

Clear- Water  Basin.  The  clear-water  basin,  into  which  the 
effluent  discharges  from  the  controllers,  is  simply  a  reinforced  con- 
crete tank  beneath  the  filters,  for  equalizing  the  load  on  the  high- 
pressure  pumps  and  furnishing  a  reserve  for  washing  filters,  etc. 
It  is  provided  with  a  sump  and  valve  for  drainage  and  cleaning. 

Washing  Filters.  In  washing  a  filter  it  is  first  shut  down  by 
closing  the  settled-water  and  effluent  valves  p  and  q  and  draining  it 
to  the  top  of  troughs  by  opening  the  sewer  valve  s,  Fig.  13.  As- 
suming the  filter  to  be  piped  for  air,  the  compressor  is  then  started 
and  the  air  valve  t  opened,  admitting  compressed  air  to  a  grid 
placed  just  below  the  surface  of  the  filter  gravel  which  distributes 
the  air  uniformly  through  the  sand  bed  by  means  of  minute  per- 
forations in  the  pipes  of  the  grid.  The  purpose  of  the  air  is  to 
loosen  the  sand,  mix  it,  and  remove  dirt  by  the  abrasion  of  the  sand 
particles.  After  three  to  five  minutes  of  air  washing  the  air  valve 
is  closed  and  the  wash  valve  u,  Fig.  13,  is  slowly  opened.  Filtered 
water  flows  from  the  wash-water  pipe  v  through  the  collector  sys- 
tem and  upward  through  the  strainer  openings,  which  are  propor- 
tioned to  give  a  uniform  upward  flow  over  the  area  of  the  filter. 
The  wash  water  flowing  upward  through  the  sand  thoroughly 
cleanses  it  and  grades  it  hydraulically,  the  dirty  water  escaping 
by  means  of  the  wash  troughs  w-w,  Figs.  12  and  13,  and  sewer 
outlet  to  the  sewer  x,  Fig.  13.  After  the  sand  is  clean  the  filter  is 
again  put  into  operation.  Washing  requires  about  12  to  15 
minutes  per  filter. 


TYPES   OF  PURIFICATION   PLANTS  47 

In  some  plants  the  air  is  omitted,  in  which  case  a  higher  wash 
velocity  is  used,  and  it  becomes  necessary  to  tie  down  the  gravel 
with  brass  screen  or  it  will  be  impelled  upward  into  the  sand  by  the 
wash  water.  In  old  plants  where  the  filter  units  consist  of  circular 
wood  or  steel  tanks,  mechanical  rakes  are  used  for  agitation  during 
washing.  Such  a  unit  is  shown  in  Fig.  18.  A  central  shaft 
carries  two  radial  arms  with  vertical  raking  bars  reaching  nearly 
through  the  sand  and  revolved  during  washing  by  suitable  gearing, 
generally  belt-driven.  The  other  details  are  readily  understood 
from  the  figure  and  correspond  to  those  already  described. 

Wash  water  may  be  obtained  by  tapping  the  wash-water  pipe 
into  a  pressure  main,  obtaining  the  required  pressure  by  means  of  a 
reducing  valve.  This  involves  a  waste  of  pressure  and  there  is 
also  danger  from  water  hammer  in  the  high-pressure  mains  due  to 
chattering  of  the  reducing  valve.  A  better  way  is  to  have  dupli- 
cate centrifugal  wash  pumps  drawing  from  the  clear-water  basin 
and  discharging  into  the  wash-water  main  at  the  proper  pressure, 
or,  better  yet,  to  have  the  pumps  discharge  into  an  elevated  tank 
of  proper  height  and  dimensions  to  insure  a  uniform  pressure. 

Valves,  Gages,  etc.  The  valves  required  per  filter  are  the 
Influent  (settled  water),  Effluent,  Wash  Water,  Sewer,  Air,  and 
Filter  Drain;  the  last  being  used  to  completely  empty  the  filter 
or  when  it  is  desired  to  waste  the  effluent.  These  are  arranged 
with  valve  stands  on  the  operating  floor,  so  as  to  form  a  convenient 
group  in  front  of  each  filter.  In  the  case  of  large  filters,  hy- 
draulically  operated  valves  are  used,  and  the  handles  for  these  are 
grouped  together  on  a  table  in  front  of  each  filter.  The  con- 
troller also  has  an  adjustment  by  which  its  rate  can  be  changed 
from  the  operating  floor.  Here,  too,  are  placed  the  loss-of-head 
gages,  one  for  each  filter,  which  indicate  the  friction  through  the 
filter,  as  already  explained  for  slow  sand  filters,  and  often  gages 
showing  the  rate  of  flow.  Each  unit  should  be  equipped  with  an 
effluent  sampling  pump,  by  means  of  which  samples  may  be  ob- 
tained at  any  time  for  analysis.  There  should  be  gages  to  show 
the  wash  and  air  pressures  and  floats  to  indicate  the  levels  of  water 
in  the  settling  and  clear-water  basins. 

Laboratory.  The  requirements  of  the  laboratory  are  quite 
simple.  The  necessary  apparatus  is  given  in  the  chapters  on 
Bacterial  and  Chemical  Tests.  As  to  the  room,  it  should  be  dry, 
well  lighted  and  ventilated,  and  provided  with  heat  and  artificial 


TYPES    OF   PURIFICATION    PLANTS  49 


LIST  OF  PARTS  IN  WOODEN  TANK  FILTER  (Fio.  18): 

1. — Loss-of-Head  Gage. 

2.— Filtered  Water  Effluent  Valve. 

3.— Wash  Water  Supply  Valve. 

4.— First  Filtered  Water  Valve. 

5.— Float  Tube. 

6.— Float  Tank. 

7.— Float. 

8. — Unfiltered  Water  Influent 

(Automatic  Control). 
9.— Orifice  Filter  Control. 
10.— Butterfly  Valve. 
11.— Float. 
12. — Agitator  Gears. 
13.— Clutch  Pulleys. 
14. — Shifting  Lever. 
15.— Waste  Wash  Water  Valve. 
16. — Agitator  Rake  Bars. 
17.— Filtering  Sand. 
18. — Filtering  Gravel. 
19. — Strainers. 
20.— Concrete  Fill. 

21.— Filtered  Water  Collecting  System. 
22. — Supply  and  Wash  Trough. 
23.— Operating  Platform. 
24.— Filtered  Water  Effluent  Pipe. 
25.— First  Filtered  Water  Pipe  to  Drain. 
26.— Wash  Water  Supply. 
27.— Waste  Water  Pipe  to  Drain. 


50 


WATER    PURIFICATION    PLANTS 


light,  preferably  steam  and  electricity.  It  should  be  provided 
with  gas  for  use  in  Bunsen  burners,  autoclave,  sterilizers,  etc. 
The  incubators  are  preferably  heated  with  electricity,  as  being 
least  troublesome.  The  principal  work  table  should  be  located 
in  front  of  a  large  window,  preferably  facing  north,  and  should 


Courtesy  Pittsburgh  Filter  Manufacturing  Co. 

FIG.  18a. — Typical  Operating  Table  Showing  Levers  for  Operating 
Hydraulic  Valves,  Recording  Loss-of-Head  Gage  (on  Left),  and  Effluent 
Sample  Pump  (on  Right). 

have  a  slate  top,  or  one  of  heavy  wood,  painted  a  dull  black. 
The  reagents  should  be  handily  placed  on  shelves  above  the  table, 
and  drawers  should  be  provided  for  filters,  test  tubes,  etc.  There 
should  be  a  sink  provided  with  hot  and  cold  water,  an  ice-box,  and 
a  water  still. 

Much  can  be  done  by  a  small  expenditure  for  extra  apparat1" 
to  expedite  the  tests.     Thus  by  using  self-filling  burettes  and 
complete  set  of  apparatus  for  each  test,  kept  ready  for  use  and  & 
up  in  definite  places  in  the  order  in  which  the  tests  are  madt, 
much  needless  walking  about  to  get  apparatus  is  done  away  with. 

There  should  be  a  desk  and  chair  for  the  chemist  and  a  filir 


GENERAL  PLAN  OF 

WASHINGTON  FILTRATION  PLANT 
SHOWING  FINISHED  SURFACES 


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City  Reservoir 


From  Trans.  American  Society  of  Civil  Engineers,  Vol.  LVII 


FIG.  19.— General  Plan  of 


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iO    o     oNo.20o    oi    o    oNo.2b    o    jo    o  No.22   o    o[    o    oN<5>.233    o   ;o    o   No.24   o    o|i 

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jooooojo    ooooo!   ooooo  ;o    oooo    oiooooo 

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o  /   Ifm    o   10    o    /    1    o    o,'    o    o  /   i  o    o  ;o    o    /   I    rrn    o!    o    o/   1  o    o 
o    /[  Ellllo    cAo    o/io    o^o    o    /ll    o     Ao    o/HdoAoo    /    mo 


Reg.Ho.  Manhole  on  Drain  Catch  Basin  R^HO. 


Ko.15 


on  Drain  to  8ew«r 


COURT    No.iD4j<L       No.3 


NO.U2T 


w     w 

).Lf28  No.L/25 


ington  Filtration  Plant  Showing  Finished  Surfaces. 


TYPES   OF   PURIFICATION   PLANTS  51 

system  for  the  records,  but  superfluous  chairs  and  furniture  are  to 
be  avoided  as  tending  to  make  the  laboratory  too  comfortable  a 
place  for  visitors. 

Mechanical  Filtration  and  Water  Softening.  The  mechani- 
cal filter  plant  is  adapted,  with  a  few  slight  alterations,  to  do 
efficient  work  in  water  softening.  The  principal  requirements  to 
fit  it  for  this  work  are  an  ample  settling  basin  and  larger  facilities 
for  storing  and  handling  coagulants,  especially  lime.  This  matter 
is  more  fully  taken  up  in  Chapter  VII,  on  Water  Softening. 

Mechanical  Filtration  and  Iron  Removal.  The  removal  of 
iron  in  conjunction  with  mechanical  filtration  is  accomplished  by 
aeration  followed  by  treatment  with  lime  and  some  aluminum 
sulphate,  as  the  precipitate  formed  by  lime  alone  is  too  fine  to  be 
readily  filtered  out.  This  is  treated  fully  in  Chapter  VI,  Coagula- 
tion and  Sterilization. 

The  Slow  Sand  Filtration  Plant  at  Washington,  D.  C.*  The 
water  supply  of.  the  City  of  Washington  is  obtained  from 
the  Potomac  River  by  a  diversion  dam  above  the  Great  Falls, 
being  conducted  thence  to  the  city  through  an  aqueduct  and  tunnel 
of  an  aggregate  length  of  90,000  feet.  Two  large  reservoirs,  each 
of  150,000,000  gallons  nominal  capacity,  are  located  along  the 
aqueduct,  and  this  terminates  in  a  third  reservoir  of  300,000,000 
gallons  capacity  situated  within  the  city  proper,  at  a  sufficient  ele- 
vation to  supply  most  parts  thereof  by  gravity,  a  few  excep- 
tionally high  points  being  supplied  by  means  of  booster  pumps. 
The  capacities  given  are  nominal,  about  300,000,000  gallons  being 
actually  available  from  the  three  reservoirs.  The  aqueduct  has  a 
capacity  of  75,000,000  gallons  per  day. 

As  considerable  sedimentation  is  secured  in  the  reservoirs,  no 
additional  basins  were  built,  the  water  being  pumped  directly 
from  the  last  (Washington  City)  reservoir  to  the  filters  which  are 
adjacent  thereto.  The  pumping  equipment  consists  of  three 
engine-driven  centrifugal  pumps,  each  of  40,000,000  gallons  per 
day  capacity,  located  in  a  pumping  station  built  as  part  of  the 
filtration  project.  The  lift  from  the  reservoir  to  the  water  level  on 
the  filters  varies  from  21  to  35  feet  as  the  reservoir  is  drawn  down. 

*  "  Works  for  the  Purification  of  the  Water  Supply  of  Washington,  D.  C." 
By  Allen  Hazen  and  E.  D.  Hardy,  Trans.  American  Society  of  Civil  En- 
gineers, Vol.  LVII,  p.  307. 


52 


WATER   PURIFICATION   PLANTS 


As  the  close  regulation  of  centrifugal  pumps  under  varying  head  is 
difficult,  allowance  was  made  for  a  fluctuation  of  6  inches  in  depth 
of  water  on  the  niters,  which  gives  an  aggregate  margin  of  4,000,000 
gallons.  The  filtered  water  is  collected  in  a  pure-water  reservoir, 


DETAIL  OF 
INTERIOR  DRAIN'S 


15  Split  Tile  Cover 
12"Split  Tile  Lateral 


19V  («-#-»: 

SECTION   Of  MAIN  COLLECTOR 
AT  LOWER  END  OF  FILTER 


PLAN  OF  UNDERDRAINAGE  SYSTEM,   SHOWING  MANHOLES,  LATERALS  AND  CONNECTIONS 
Scale  of  Feet 


SECTION  ON  A-B 
From  Trans.  American  Society  of  Civil  Engineers,  Vol.  LVII. 

FIG.  20.— Details  of  Filters,  Washington,  D.  C. 

roofed  with  a  concrete  groined-arch  construction,  of  14,000,000 
gallons  capacity,  whence  it  is  supplied  to  the  city  through  a  set  of 
equalizing  float  valves. 

The  arrangement  of  the  plant  is  shown  by  Fig.  19.  It  is  ir- 
regular, as  the  available  ground  was  limited  and  had  to  be  used 
most  economically.  There  are  twenty-nine  filters,  each  having  one 
acre  of  sand  area,  so  that  at  the  customary  rate  (3,000,000  gallons 


TYPES    OF    PURIFICATION    PLANTS 


53 


per  acre  per  day)  the  plant  has  a  daily  capacity  of  87,000,000 
gallons.  Allowance  must  be  made,  however,  for  niters  out  of  use 
due  to  sand  scraping  and  repairs.  It  will  be  noted  that  the  filters 


EIev.C.L.(157.3) 
lo'Refill  Elev.  (156.3_) 


SoViltered  Water  Effluent  .Venturl  Meter    .' ', 


/Etev.(  152.2) 


y-^a. v,-^//    ~&y 

SECTION  ON  c-C   1GC-LDraIn  EleT-  °fC.L.(151} 


Dry  Chamber  for  Indicator  Apparatus 
Bpec.  F 


Tenturi  Meter 


Main  Etfuent  for  Filtered  Water 


NOTE:- 

Detail  arrangements  differ  slightlj 
in  the  different  houses 


PLAN  AND  SECTIONS 

REGULATOR  HOUSES 


Main  Effluent  for  Filtered  W: 


SECTION  ON  D-D 
From  Trans,  American  Society  of  Civil  Engineers,  Vol.  LVII, 

FIG.  21. 


are  grouped  on  each  side  of  "  courts  "  which  contain  the  piping, 
sand-washing  apparatus,  etc. 

The  niters  are  essentially  of  the  type  already  described,  the 
principal  features  being  shown  by  Fig.  20.  The  walls,  floor,  and 
groined-arch  roof  construction  are  of  concrete  masonry,  the  type  of 


Engineering  Record,  Apnl  7, 1906. 

FIG.  22.— Sand  Storage  Bins,  Washington,  D.  C.,  Filtration  Plant. 


Engineering  Record,  April  7, 190o. 

FIG.  23.— Sand  Washers,  Washington  Filtration  Plant 


TYPES    OF    PURIFICATION    PLANTS 


55 


structure  being  such  as  to  require  little  reinforcement.  The  roof 
is  covered  with  earth  and  sodded.  The  central  collecting  pipe  is 
located  below  the  floor  level,  and  the  filtered  water  is  led  to  it  by 


SECTION  OF  MODIFIED  FOUNDATION 


SAND  BINS 


REINFORCING  IN  BOTTOM 
OF  CONE 

Trans.  American  Society  of  Civil  Engineers,  Vol.  LVII. 

FIG.  24. — Details  of  Sand  Bins,  Washington  Filtration  Plant. 

'lateral  drains  of  12-inch  half-tile  and  6-inch  tile,  the  latter 
being  used  near  the  extremities  of  the  laterals.  A  peculiarity  of 
construction  consists  in  the  interposition  of  a  brass  orifice  plate  at 
the  junction  of  laterals  and  main  collector  for  the  purpose  of  com- 
pensating for  variations  in  loss  of  head  between  those  laterals 


Trans.  American  Society  of  Civil  Engineers,  Vol.  LVII. 

FIG.  25.— Interior  View  of  Filter,  Washington  Filtration  Plant  (Showing 
Filter  Sand  and  Gravel  Removed).   Note  Lateral  Drains. 


Trans.  American  Society  of  Civil  Engineers,  Vol.  LVII. 

FIG.  26. — General  View  of  Washington,   D.  C.,  Filtration  Plant. 


TYPES    OF    PURIFICATION    PLANTS  57 

remote  from  and  those  adjacent  to  the  filter  outlet.  The  drain- 
age system  is  covered  with  12  inches  of  graded  gravel  supporting 
40  inches  of  filter  sand  (effective  size,  0.32  mm. ;  uniformity  coef- 
ficient, 1.77).  The  working  head  of  water  on  the  filters  is  4  feet. 

The  effluent  pipes  from  the  filter  units  are  carried  to  centrally 
located  regulator  houses,  of  which  there  are  seven,  generally  ar- 
ranged to  serve  five  filters  each.  Fig.  21  gives  the  details  of  one 
such  house.  The  substructure  contains  six  water-tight  concrete 
compartments,  five  serving  as  receiving  basins  for  the  effluent  of 
the  filters,  the  sixth  containing  recording  mechanism.  The  filter 
effluents  enter  the  respective  compartments  through  Venturi 
meters  and  valves  with  graduated  handwheels.  The  Venturi 
meters  indicate  and  record  the  rates  of  filtration  for  each  filter,  and 
adjustments  of  rate  are  made  by  means  of  the  graduated  valves. 
The  effluents  discharge  into  a  central  collecting  flume  through 
valved  apertures  and  are  carried  to  the  filtered-water  reservoir  via 
a  main  effluent  pipe.  Facilities  for  draining  any  compartment  are 
provided.  The  superstructure  is  of  brick  with  stone  trimming  and 
tile  roof. 

The  method  of  handling  and  washing  -sand  is  that  already  de- 
scribed, and  the  reader  is  referred  to  Figs.  5  and  6  for  details  of  the 
portable  sand  ejectors  and  sand  washers  used.  Fig.  22  illustrates 
one  of  the  sand  storage  bins,  of  which  there  are  twenty-nine.  In 
the  left  background  is  the  superstructure  of  one  of  the  regulator 
houses,  and  to  the  right  is  the  entrance  to  one  of  the  "  ramps  "  or 
inclined  walkways  leading  into  the  filters.  Fig.  24  shows  the  de- 
tails of  a  sand  bin.  It  is  built  so  that  a  wagon  can  drive  under- 
neath, be  filled  with  clean  sand,  which  is  then  delivered  into  the 
filters  through  manholes  in  the  roof. 

An  administration  building  contains  general  offices,  chemical 
and  bacterial  laboratories,  lockers,  toilets,  storerooms,  etc. 

While  no  provision  was  made  for  coagulation,  because  of  popular 
prejudice  against  the  use  of  chemicals,  the  advantages  to  be 
gained  therefrom  were  fully  appreciated  by  the  designing  en- 
gineers and  recent  experimental  work  at  the  plant  has  more  than 
fulfilled  anticipations  as  to  the  value  of  coagulation.  Improve- 
ments in  sand  washing  have  also  been  made,  notably  in  sub- 
stituting the  ejector  method  for  the  use  of  carts  in  replacing  sand 
in  the  filters. 

The  plant  was  built  under  the  direction  of  Colonel  A.  M. 


58 


WATER   PURIFICATION   PLANTS 


Miller,  assisted  by  Capt.  W.  P.  Wooten  and  R.  D.  Chase.  Mr. 
Allen  Hazen  was  consulting  engineer  and  Mr.  E.  D.  Hardy  has 
had  charge  of  the  plant  since  its  completion. 

The  Torresdale  Preliminary  Filters  at  Philadelphia,  Perm.* 

The  City  of  Philadelphia  has  installed  a  number  of  rapid  sand- 
filter  plants,  with  the  object  of  removing  the  coarse  suspended 


Engineering  Record,  November  14, 1908. 

FIG.   27. — Torresdale   Filtration   Plant.     Plan   and   Part   Section. 

matter  from  the  water  preliminary  to  final  filtration.  Of  these 
the  installation  at  Torresdale  is  typical.  The  original  plant  was  of 
the  slow  sand  type,  similar  to  that  at  Washington,  already  de- 
scribed, and,  filtering  at  a  rate  of  3,000,000  gallons  per  acre  per  day, 

*  Engineering  Record,  November  14,  1908. 


TYPES    OF    PURIFICATION    PLANTS  59 

had  a  daily  capacity  of  120,000,000  gallons.  While  the  quality 
of  effluent  was  satisfactory,  it  was  desired  to  increase  the  capacity 
of  the  filters.  By  means  of  the  preliminary  filter  plant  here  de- 
scribed, it  became  possible  to  double  the  rate  of  filtration  of  the  slow 
sand  filters,  enabling  an  output  of  240,000,000  gallons  per  day  to 
be  obtained. 

The  preliminary  filters  are  adjacent  the  original  slow  sand 
plant,  are  of  240,000,000  gallons  capacity,  and  essentially  of  the 
mechanical  type,  although  somewhat  simplified  and  operated 
without  coagulation.  As  shown  by  Fig.  27,  the  plant  consists  of 
120  beds,  arranged  in  8  rows  of  15  beds  each.  Each  bed  measures 
20  feet  3  inches  by  60  feet,  has  a  capacity  of  2,000,000  gallons  per 
day  when  operated  at  the  rate  of  80,000,000  gallons  per  acre  per 
day,  and  has  a  complete  system  of  control  valves  and  piping, 
manipulated  by  levers  on  an  individual  operating  table.  There 
are  four  filter  houses,  one  between  each  double  row  of  filters.  The 
raw  water  is  admitted  to  the  filters  by  means  of  channels  or 
gullets  between  the  rows  of  filters,  entering  at  the  center  of  the  rear 
wall,  and  after  filtration  is  collected  in  effluent  gullets  under  the 
filter  houses. 

The  filters,  flumes,  floors,  roofs,  etc., .are  of  concrete,  reinforced 
or  supported  by  structural  shapes.  The  superstructure  is  of  face 
brick  trimmed  with  gray  granite. 

The  raw  water  is  pumped  to  the  preliminary  filters  from  the 
river  through  an  11-foot  riveted  steel  conduit  encased  in  concrete. 
This  conduit  runs  the  full  length  of  the  filter  plant  and  has  three 
7-foot  and  two  53/2-foot  steel  branch  connections,  leading  to  the 
five  influent  gullets  already  mentioned.  These  influent  gullets 
extend  the  full  width  of  the  plant,  between  adjacent  rows  of 
filters,  being  formed  by  the  back  walls  of  the  filter  units,  except 
the  two  outside  gullets,  where  an  additional  wall  had  to  be  added. 
The  raw  water  enters  the  filter  beds  by  means  of  cast-iron  pipes 
in  the  rear  wall,  each  controlled  by  a  16-inch  hydraulic  valve 
located  in  the  central  wash  gutter.  This  is  formed  in  the  cus- 
tomary way  by  two  reinforced  concrete  walls  extending  longi- 
tudinally through  the  center  of  the  filter  and  12  inches  apart, 
dividing  the  filter  bed  proper  into  two  equal  portions.  Steel  wash- 
water  troughs  extend  laterally  across  the  filters  at  right  angles  to 
and  level  with  the  tops  of  the  central  gutter  walls,  and  serve  to 
convey  the  wash  water  to  the  central  gutter,  whence  it  finds  its 


60 


WATER    PURIFICATION    PLANTS 


way  to  the  sewer  through  a  hydraulically  operated  sluice  gate 
at  the  front  end  of  the  filter.  There  are  twelve  such  wash-water 
troughs  per  filter,  being  spaced  equally,  six  on  each  side  of  the 
central  gutter.  The  general  arrangement  of  central  gutter 
troughs,  etc.,  is  shown  in  Fig.  28. 

The  filtering  material  consists  of  gravel  and  sand  of  graded 
sizes,  decreasing  in  size  upward,  viz.,  at  the  bottom,  15  inches  of 
gravel,  varying  in  size  from  2  to  3  inches;  4  inches  of  gravel  from 


Engineering  Record,  November  14, 1908. 

FIG.  28.— Torresdale  Filtration  Plant.    View  of  Filter  Bed. 


%  to  !}/£  inches;  3  inches  of  gravel  from  J4  to  J/£  inch;  8  inches 
from  J4  to  J/8  inch,  and  a  top  coating  of  12  inches  of  sand  from 
0.8  to  1  mm.  size.  Under  the  gravel,  and  running  longitudinally 
through  the  center  of  each  of  the  two  equal  filter  beds  into  which 
the  unit  is  divided  by  the  cross  walls,  is  an  effluent  collector  formed 
by  half  tile  of  concrete,  with  slotted  openings  for  admission  of  the 
filtered  water.  The  two  lines  of  tile  unite  for  each  filter,  allowing 
the  filtered  water  to  flow  through  a  short  length  of  16-inch  pipe  and 
via  an  automatic  rate  controller  into  the  effluent  gullet  situated 
between  each  two  rows  of  filters.  Each  filter  outlet  is  equipped 
with  an  hydraulically  operated  valve.  The  main  effluent  gullets 
terminate  in  7-foot  steel  conduits  leading  to  an  11-foot  steel,  con- 


TYPES   OF   PURIFICATION    PLANTS  61 

crete-cased  head  conduit,  through  which  the  water  passes  on  to  the 
slow  sand  niters. 

For  washing  the  filters,  water  and  air  are  used,  and  a  separate 
system  of  piping  is  provided.  Filtered  water  is  pumped  into  an 
elevated  wash-water  tank,  built  of  reinforced  concrete,  from  which 
a  48-inch  wash-water  line  leads  to  the  plant,  a  30-inch  branch 
line  from  which  extends  through  the  pipe  gallery  between  each  two 
rows  of  filters.  At  the  center  of  each  filter  there  is  a  20-inch  wash- 
water  take-off  controlled  by  a  hydraulic  valve.  This  20-inch 
line  extends  longitudinally  through  the  filter,  being  hung  from  the 
roof  above  the  central  gutter,  and  divides  at  the  center  of  the  bed 
into  four  12-inch  distributing  pipes,  from  each  of  which  two  8-inch 
down  pipes  take  off,  leading  to  8-inch  manifold  headers  placed 
above  the  filtered  water  collectors  (below  the  sand  and  gravel). 
The  manifold  proper  consists  of  IJ^-inch  lateral  pipes,  spaced  5% 
inches  on  centers  and  drilled  with  /i6-inch  holes  on  the  bottom. 
This  effects  an  essentially  equal  distribution  of  the  wash  water 
under  the  gravel,  which,  rising  upward  through  the  sand,  cleanses 
the  same  of  its  collected  impurities,  the  dirty  wash  water  over- 
flowing into  the  collecting  troughs,  thence  to  the  central  gutter, 
and  out  into  the  wash-water  drain,  which  consists  simply  of  the 
space  between  the  filter  walls  and  the  effluent  gullet.  Air  agita- 
tion is  used  during  washing,  being  supplied  by  an  air  main  in  each 
gallery,  with  branches  to  the  individual  filters  connected  into  the 
wash-water  header,  the  same  manifold  being  used  for  distributing 
wash  water  and  air.  A  6-inch  valve  is  provided  for  draining  each 
filter. 

Fig.  29  shows  a  section  through  one  of  the  filter  galleries.  At 
each  side  are  the  front  walls  of  opposite  filter  units.  The  filter 
floor  is  carried  through  as  the  gallery  floor.  In  the  center,  ex- 
tending longitudinally  through  the  gallery,  is  the  effluent  gullet  or 
flume,  6  by  6  feet  in  area,  into  which  the  filtered  water  discharges 
through  an  effluent  controller.  The  top  of  this  flume  supports  the 
30-inch  wash  header  and  above  that  the  operating  platform. 
The  air  pipe  is  suspended  from  the  ceiling,  and  at  each  filter  a 
12-inch  branch  is  taken  off  connecting  into  the  20-inch  wash- 
water  pipe.  The  air  supply  is  controlled  by  a  12-inch  hydraulic 
valve.  The  spaces  between  the  filter  walls  and  effluent  gullet 
form  the  wash-water  drains,  and  the  central  gutters  and  drain 
pipes  discharge  directly  into  these. 


62 


WATER   PURIFICATION    PLANTS 


This  plant  is  of  special  type,  designed  for  a  definite  purpose, 
namely,  to  prefilter  the  water  only,  and  the  design  is  not  adapted 
for  more  general  use.  The  plant  was  designed  and  constructed 


8  Pressure 
-Effluent  ContrplU 
T~4"steam 

Return 


CROSS  SECTION  THROUGH  FILTER  HOUSE 
Engineering  Record,  November  14, 1908. 

FIG.  29.— Torresdale  Filtration  Plant. 

under  the  direction  of  Mr.  Fred  C.  Dunlap,  chief  of  the  Bureau 
of  Water,  Philadelphia,  Perm. 

The  Mechanical  Filtration  Plant  at  Minneapolis,  Minn.*  This 
plant  is  of  interest  as  being  typical  of  the  modern  installation  of 
larger  size,  because  of  its  flexibility  of  operation,  made  necessary 
by  the  rapid  variations  of  the  Mississippi  River,  from  which  the 

*  Engineering  Record,  November  18,  1911. 


TYPES    OF    PURIFICATION    PLANTS 


63 


raw-water   supply    is   derived,    and   because   of    its   method    of 
handling  and  mixing  chemicals. 

The  nitration  plant  is  built  near  two  old  service  reservoirs, 
each  of  47,000,000  gallons  capacity.  One  of  these  was  built  up  10 
feet  and  adapted  as  a  preliminary  settling  basin,  to  which  the  raw 
water  is  pumped  and  allowed  to  settle  (approximately  24  hours) 


Engineering  Record,  November  18,1911. 
FIG.  30. — Minneapolis  Filtration  Plant.    General  Plan. 

before  reaching  the  nitration  plant.  The  other  reservoir  was 
roofed  over  with  a  groined  arch  construction  of  reinforced  concrete, 
and  serves  as  a  clear-water  reservoir,  receiving  the  effluent  of  the 
filter  plant  and  equalizing  the  load  on  the  filters,  a  very  desirable 
feature.  The  normal  rating  of  the  plant  is  39,000,000  gallons  per 
day. 

The  general  layout  of  the  plant  is  shown  hi  Fig.  30.  After 
passing  through  the  preliminary  settling  basin,  the  water  flows 
through  a  60-inch  cast-iron  line  to  a  controlling  chamber,  entering 
the  same  through  a  Venturi  meter,  which  measures  and  records 
the  volume  and  actuates  the  chemical  feed  controls,  causing  an 
automatic  adjustment  of  the  amount  of  coagulant  to  the  raw  water 


64  WATER    PURIFICATION    PLANTS 

to  be  treated.  The  controlling  chamber  is  provided  with  sluice 
gates,  so  that  the  raw  water  may  pass  from  it  either  into  the  mixing 
chamber  or  directly  into  the  coagulating  basins ;  other  sluice  gates 
provide  for  passing  it  directly  to  the  filters  or  allowing  some  of  it 
to  waste  through  a  20-inch  cast-iron  pipe  line  intended  for  flushing 
sediment  from  the  floor  of  the  coagulating  basins. 

Normally  the  water  passes  from  the  controlling  to  the  mixing 
chamber,  the  coagulant  solutions,  aluminum  sulphate  and  lime 
(when  required)  being  introduced  at  this  point.  The  mixing 
chamber  is  a  covered  structure  of  reinforced  concrete,  34  feet 
8  inches  wide  by  173  feet  long  inside,  with  wooden  baffles  of  the 
vertical  type,  3  feet  center  to  center.  The  water  passes  back  and 
forth  between  the  baffles  in  its  journey  through  the  mixing  cham- 
ber, traveling  a  total  distance  of  about  2,000  feet.  This  insures  a 
thorough  mixing  of  the  coagulants  with  the  water  and  allows  time 
for  the  chemical  reactions  to  take  place.  The  mixing  chamber  is 
built  across  the  ends  of  the  coagulating  basins,  with  a  space  of 
about  73/2  feet  between  the  two,  this  space  being  denoted  on  the 
drawing,  Fig.  30,  as  the  center  passage.  This  center  passage  is 
divided  by  horizontal  diaphragms  of  concrete  into  two  flumes  or 
conduits,  the  side  wall  of  the  mixing  chamber  and  the  end  walls  of 
the  coagulating  basins  forming  the  vertical  sides  of  the  flumes. 
The  lower  flume  receives  the  water  from  the  mixing  chamber  and 
introduces  it  into  the  coagulating  basins.  As  it  may  not  always  be 
desirable  to  run  the  water  through  the  full  length  of  the  mixing 
chamber,  four  sluice  gates  are  located  in  the  west  wall  of  same, 
communicating  directly  with  the  lower  flume  and  thence  with  the 
coagulating  basins.  As  already  stated,  the  water  may  enter  the 
lower  flume  at  the  north  end,  directly  from  the  controlling  chamber, 
thus  by-passing  the  mixing  chamber.  The  upper  flume  receives 
the  water  after  its  passage  through  the  basins  and  conducts  it  to 
the  filters.  It  may  also  receive  the  water  directly  from  the  con- 
trol chamber  or  after  its  passage  through  the  mixing  chamber. 
Further  gates  provide  for  by-passing  either  basin,  or  operating  the 
basins  both  in  series  or  parallel.  The  extreme  flexibility  and 
absence  of  complicated  pipe  work  in  this  arrangement  are  commend- 
able. Below  the  central  passage  is  a  12-inch  sewer  into  which 
both  the  mixing  and  controlling  chambers  and  the  coagulating 
basins  may  be  drained. 

After  passing  through  the  mixing  chamber,  the  treated  water 


TYPES   OF   PURIFICATION    PLANTS  65 

enters  the  coagulating  basins.  These  are  in  duplicate,  each  mea- 
suring 95  feet  8  inches  by  119  feet  4  inches  inside,  and  have  a  com- 
bined capacity  of  about  2,800,000  gallons.  Each  basin  has  three 
vertical  concrete  baffles  with  water  passages  around  the  ends,  so 
that  the  water  makes  four  passes  in  traversing  the  basin.  The 
basins  can  be  flushed  by  by-passing  raw  water  from  the  controlling 
chamber  through  the  20-inch  flushing  line  already  mentioned, 
being  drained  off  through  sumps  leading  to  the  12-inch  cast-iron 
drain  under  the  central  passage.  Additional  fire-hose  connections 
are  provided  for  hosing  out  the  heavy  sludge. 

The  water,  after  passing  through  the  coagulating  basins,  enters 
the  upper  flume  over  a  skimming  weir,  through  which  it  passes 
into  a  60-inch  influent  pipe,  leading  to  the  filters.  These  are  twelve 
in  number,  six  on  either  side  of  the  operating  gallery,  and  have 
each  a  capacity  of  3,250,000  gallons  at  a  rate  of  125,000,000  gallons 
per  acre  per  day.  Each  bed  is  divided  into  two  parts  by  central 
wash-water  gutter  of  the  usual  type,  which,  in  conjunction  with 
eight  lateral  gutters,  serves  to  distribute  the  settled  and  treated 
water  entering  the  filter  through  a  twenty-inch  valved  branch  con- 
nection from  the  60-inch  influent  header  in  the  gallery. 

The  filtering  medium  consists  of  30  inches  of  sand  having  an 
effective  size  from  0.35  to  0.44  mm.  and  a  uniformity  coefficient 
of  1.65.  The  strainer  system  consists  of  concrete  ridges  cast  on 
the  bottom  of  the  filter  at  right  angles  to  the  central  gutter.  -The 
grooves  between  the  ridges  are  filled  with  graded  gravel  and  a 
brass  screen  is  bolted  over  the  gravel  to  prevent  displacement 
while  washing.  The  gravel  rests  on  perforated  brass  strainer 
plates,  below  which  are  water  passages  for  collecting  the  effluent 
and  distributing  the  wash  water.  The  filtered  water  collected  by 
the  strainer  system  flows  into  a  manifold  of  collector  pipes,  and 
through  these  and  a  rate  controller  into  the  clear-water  basin 
beneath  the  filters. 

The  filters  are  washed  by  forcing  filtered  water  under  pressure 
upward  through  the  strainer  system.  No  air  is  used,  the  wash 
pressure  being  sufficient  to  thoroughly  agitate  and  cleanse  the 
sand.  The  rate  of  wash  is  15  gallons  per  square  foot  per  minute. 
The  dirty  wash  water  is  collected  by  the  cross  troughs  and  flows 
into  the  central  gutter,  thence  through  a  valved  connection  into  a 
reinforced  concrete  sewer  beneath  the  filter  gallery.  As  no  large 
sewer  was  available,  the  dirty  wash  water  is  collected  in  a  receiving 


66 


WATER   PURIFICATION    PLANTS 


basin,  and  slowly  drained  away  through  a  12-inch  sewer.  Water 
for  washing  is  obtained  from  an  elevated  tank  of  reinforced  con- 
crete, located  above  the  receiving  basin  just  mentioned.  The 
capacity  of  this  tank  eliminates  the  necessity  for  large  wash  pumps, 
as  it  can  be  filled  between  washings  by  relatively  small  pumps,  in 


SECTION  THROUGH  CHEMICAL  STORAGE  BINS  AND  DETAIL  OF  AGITATOR. 
Engineering  Record,  November  18, 1911. 

FIG.  31. — Minneapolis  Filtration  Plant. 

the  present  case  by  two  centrifugals  of  1,600  gallons  per  minute 
capacity. 

Special  interest  attaches  to  the  arrangements  for  handling  and 
mixing  chemicals.  The  necessary  apparatus  is  contained  in  a 
head  house  located  across  one  end  of  the  filter  building.  The 


TYPES    OF    PURIFICATION    PLANTS 


67 


Engineering  Record,  November  18,1911. 

FIG.  32. — Minneapolis  Filtration  Plant.     Plan  of  Head  House. 


68  WATER    PURIFICATION    PLANTS 

floor  elevations  are  such  that  the  chemicals  can  be  handled  and 
stored  by  gravity,  but  the  solutions  must  be  pumped  to  the  orifice 
boxes  which  feed  them  into  the  mixing  chamber. 

The  lime  and  alum  are  purchased  in  carload  lots  and  carted  to 
the  plant  by  wagons.  The  wagons  discharge  upon  a  dumping 
platform  shown  on  the  left-hand  side  of  Fig.  31,  at  elevation  328.0. 
The  lime  and  alum  pass  from  this  platform  through  separate 
chutes  to  the  boot  of  a  bucket  elevator,  the  lime  passing  en  route 
through  a  small  crusher,  which  breaks  it  into  lumps  of  a  size  readily 
handled  by  the  elevator.  The  material  is  raised  by  the  elevator 
into  a  hopper  at  the  top  of  the  building  and  discharges  through  a 
grain  chute  equipped  with  a  revolving  spout  capable  of  discharging 
into  any  one  of  12  reinforced  concrete  storage  bins.  In  event  of  a 
breakdown  in  the  bucket  elevator,  a  freight  elevator  of  standard 
design  may  be  used  to  raise  the  chemicals  from  the  unloading 
platform  to  the  top  of  the  storage  bins,  into  which  they  are  then 
shoveled  by  hand  labor.  Below  the  bins  a  traveling  bucket 
operates  on  a  suspended  rail  and  serves  to  convey  the  coagulant  to 
the  solution  tanks.  The  arrangement  of  the  tracks  is  shown  in 
Fig.  32.  The  traveling  bucket  is  balanced  on  a  scale  beam, 
enabling  the  operator  to  measure  out  the  required  amount  of 
chemical  directly  from  the  bins. 

The  lime-slaking  apparatus  is  rather  unique,  consisting  of  two 
concrete  mixers,  each  of  \Y^  yards  capacity,  into  which  the  lime 
is  dumped  directly  from  the  traveling  bucket.  Water  is  added 
and  the  mixture  revolved  in  the  drum  of  the  machine.  The  milk 
of  lime  discharges  into  a  trough  having  valved  outlets  into  each  of 
the  three  lime  solution  tanks.  These  are  circular  steel  tanks, 
12  feet  5  inches  in  diameter  and  13  feet  deep.  Steel  is  used,  be- 
cause calcium  hydroxid  has  a  destructive  action  on  concrete.  The 
alum  and  hypo  tanks,  however,  are  of  concrete  and  rectangular  in 
plan.  The  agitating  device  employed  in  each  of  the  several  tanks 
consists  of  a  helicoidal  bronze  impeller  mounted  on  a  vertical  shaft 
driven  by  a  motor  at  the  top  of  the  tank.  The  direction  of  rota- 
tion is  such  as  to  create  a  downward  current  at  the  center  of  each 
tank,  driving  the  solution  along  the  floor  of  the  tank  and  up  the 
sides.  This  course  of  the  solution  is  further  aided  by  a  conical 
baffle  placed  over  the  impeller. 

The  aluminum  sulphate  is  dissolved  previous  to  discharge  into 
the  solution  tanks  in  concrete  dissolving  boxes,  6  by  3  feet  in  plan 


TYPES   OF    PURIFICATION    PLANTS  69 

and  4  feet  deep,  which  are  provided  in  duplicate.  Agitation  in 
these  boxes  is  provided  for  by  a  manifold  of  1-inch  galvanized  pipe 
at  the  bottom  drilled  with  /i6-inch  holes  3  inches  on  centers. 
Water  flowing  upward  through  this  grid  dissolves  the  alum  more 
readily  than  the  usual  downward  stream.  The  dissolved  alum 
overflows  from  these  boxes  and  passes  into  the  solution  tanks 
through  a  screened  opening. 

An  attempt  is  made  in  this  plant  to  overcome  the  hardship 
which  usually  attaches  to  the  handling  of  the  hypochlorite  of  lime 
used  for  disinfection  of  the  filtrate.  The  device  used  is  shown  in 
Fig.  31.  The  hypo  is  received  in  drums  weighing  about  750 
pounds.  The  drums  are  lowered  to  the  operating  floor  by  means 
of  the  freight  elevator  and  rolled  under  an  I-beam  traveler, 
running  across  the  hypo  dissolving  boxes.  The  drum  is  lifted 
into  the  dissolving  box  by  means  of  a  set  of  chain  blocks,  coming 
to  rest  on  a  false  bottom  of  perforated  grate  bars.  The  dis- 
solving box  is  then  filled  with  water  so  as  to  submerge  the  drum 
completely.  While  the  drum  rests  on  the  grate  bars,  holes  are 
driven  in  both  ends  by  steel  pins;  a  single  pin  embedded  in  one  end 
of  the  dissolving  box  is  driven  into  the  exact  center  of  one  end  of 
the  drum,  while  the  other  end  is  perforated  by  four  pins  mounted 
on  a  chuck  rotating  on  a  steel  shaft  passing  through  the  end 
of  the  dissolving  box  by  means  of  a  stuffing  gland.  Besides  its 
rotary  motion,  the  shaft  can  move  longitudinally  through  the 
gland  and  the  can  is  perforated  by  striking  the  end  of  the  shaft 
with  a  sledge,  causing  the  four  pointed  pins  in  the  chuck  to  per- 
forate one  end  of  the  drum,  and  driving  the  drum  bodily  against 
the  center  pin  at  the  other  end.  The  drum  can  now  be  rotated 
by  turning  the  shaft  through  agency  of  a  ratchet  and  is  cut  in 
two  under  water  by  a  large  can  opener.  The  hypo  is  then  dis- 
solved out  by  the  same  type  of  manifold  device  used  in  the  alum 
dissolving  boxes  and  flows  into  the  hypo  solution  tanks. 

As  the  coagulant  leaves  the  solution  tanks  at  a  level  much 
below  that  of  the  water  in  the  mixing  chamber,  it  is  pumped  to 
chemical  control  devices  by  small  bronze  centrifugal  pumps. 
The  chemical  feed  tanks  are  located  on  the  ground  floor.  The 
solutions  are  pumped  into  them  at  a  constant  rate,  a  uniform  head 
being  maintained  by  overflows  in  the  tanks  which  carry  the  sur- 
plus back  into  the  respective  solution  tanks.  The  chemical  feed 
controllers  consist  of  adjustable  orifices  automatically  regulated 


70 


WATER   PURIFICATION    PLANTS 


by  the  difference  in  head  of  the  Venturi  meter  in  the  controlling 
chamber,  so  that  the  amount  of  coagulant  is  always  proportional 
to  the  rate  of  raw-water  pumpage.  The  lime  is  applied  as  the 


Engineering  Record,  November  18,1911. 

FIG.  33. — Minneapolis  Filtration  Plant.    Solution  Tanks,  Overhead 
Conveyor,  and  Controllers. 

water  enters  the  mixing  chamber,  the  alum  a  little  later  at  some 
point  in  the  central  passage.  The  hypo  is  added  as  the  water 
enters  the  clear-water  reservoir. 

This  plant  was  designed  by  Hering  &  Fuller,  consulting  en- 


TYPES    OF    PURIFICATION    PLANTS 


71 


gineers,  New  York.  Mr.  Andrew  Rinker,  city  engineer,  had 
supervision  of  the  construction  with  Mr.  W.  N.  Jones  in  direct 
charge,  assisted  by  Mr.  J.  A.  Jensen,  waterworks  engineer.  Mr. 
J.  W.  Armstrong  had  immediate  charge  of  plans  and  specifications 
for  the  consulting  engineers. 

The  Mechanical  Filter  Plant  at  Wilkinsburg,  Penn.*  This 
is  a  type  of  plant  peculiarly  adapted  to  very  hilly  or  semi- 
mountainous  regions  where  the  location  is  adjacent  to  a  high  pres- 
sure reservoir  and  rather  difficult  of  access.  In  this  instance  the 
plant  is  located  on  a  hill  top  about  one  mile  from  the  Allegheny 
River  (the  source  of  supply)  and  about  600  feet  above  same.  The 
water  is  pumped  directly  from  the  river  to  the  sedimentation 
basins  against  a  total  pressure  of  250  pounds  per  square  inch. 


PLAN  OF  MECHANICAL  FILTRATION  PLANT,  WILKINSBURG,  PA. 
Engineering  Record,  October  1,  1910. 

FIG.  34. 

The  plant  comprises  two  uncovered  sedimentation  basins  of  re- 
inforced concrete,  each  150  feet  long,  60  feet  wide,  and  22J/£  feet 
deep,  and  10  filter  beds,  each  having  a  capacity  of  1,250,000  gallons 
per  day,  making  the  total  plant  capacity  12,500,000  gallons  daily. 
The  water  enters  the  sedimentation  basins  through  cast-iron 
manifolds  terminating  in  6-inch  aerating  pipes,  and  is  collected 
at  the  outlet  end  of  the  basins  by  a  reinforced  concrete  flume  con- 
necting with  a  cast-iron  pipe  which  delivers  the  coagulated  and 

*  Engineering  Record,  October,  1910. 


72  WATER    PURIFICATION    PLANTS 

settled  water  to  the  filters.  The  general  arrangement  of  plant  is 
shown  by  Fig.  34. 

The  filters  are  housed  in  a  long  brick  building,  being  arranged 
five  on  each  side  of  a  central  pipe  gallery.  •  The  equipment  is 
of  standard  design.  The  effluent  and  wash-water  manifold  is 
entirely  of  cast  iron  with  cast-iron  laterals  and  brass  strainers, 
and  above  this  are  placed  8  inches  of  gravel  and  36  inches  of  sand. 
Air  agitation  is  used,  the  air  manifold  being  below  the  gravel  and 
consisting  of  small  perforated  brass  tubes  supplied  through  a 
central  header  pipe.  The  wash-water  troughs  are  of  cast  iron,  ex- 
tending laterally  from  a  central  gutter  of  the  usual  type  and  are 
designed  to  handle  10  gallons  of  wash  water  per  minute  per  square 
foot  of  sand  area.  The  effluent  controllers  are  of  the  velocity 
type,  similar  in  principle  to  the  one  previously  described.  All 
valves  are  hydraulically  operated,  the  handles  for  each  filter  being 
grouped  on  an  enclosed  marble  operating  table.  This  table  also 
contains  the  loss-of-head  gage,  which  is  of  the  registering  type,  two 
pens  recording  the  head  on  the  filter  and  the  draft  on  the  effluent 
pipe  upon  a  moving  chart,  clock-driven.  Fig.  35  shows  a  general 
view  of  the  operating  gallery  and  tables.  The  interior  walls  are 
of  buff  fire-flashed  brick  and  the  whole  presents  a  very  neat  and 
sanitary  appearance.  In  the  general  office,  a  marble  sample 
table  is  located  on  which  are  mounted  glass  tubes  and  spigots,  one 
for  each  filter,  and  one  each  for  the  raw  and  treated  water.  Sample 
streams  from  the  respective  sources  are  kept  constantly  circulating 
through  these  by  individual  J^-inch  centrifugal  pumps,  so  that  the 
operator  has  constantly  on  view  and  on  tap  water  from  all  the 
units  of  the  plant.  The  effluent  discharges  through  the  controller 
into  a  reinforced  concrete  conduit  leading  to  Reservoir  No.  1. 

At  the  east  end  of  the  filter  building  and  integral  therewith 
is  the  head  house,  having  three  floors:  a  basement,  level  with  the 
pipe  gallery,  a  main  floor  at  the  operating  platform  level,  and  a 
second  floor.  The  basement  contains  piping;  air,  wash,  and  pres- 
sure pumps,  sampling  pumps,  electric  generating  and  heating 
plants.  The  main  floor  contains  the  solution  tanks  and  orifice 
boxes,  the  main  entrance  or  lobby,  general  office,  and  laboratories. 
The  office  and  laboratories  are  floored  and  wainscoted  with  white 
tile  and  have  a  steel  ceiling.  The  lobby  contains  the  stair  well, 
leading  to  the  basement  and  second  floor,  the  main  switchboard, 
and  the  more  important  gages. 


74  WATER   PURIFICATION    PLANTS 

The  second  floor  is  devoted  to  storing,  handling,  and  mixing 
the  coagulants.  The  upper  ends  of  the  solution  tanks,  located  on 
the  floor  below,  project  through  to  this  level  for  charging  purposes. 
Lime,  alum,  and  hypo  tanks  are  provided  in  duplicate,  each  being 
equipped  with  a  concrete  solution  box  having  a  screened  outlet  into 
the  tank.  Owing  to  the  isolated  location  of  the  plant,  the  chemicals 
must  be  brought  up  by  wagons,  which  deliver  at  one  end  of  the 
head  house.  The  barrels  or  sacks  of  coagulant  are  handled  by 
means  of  a  trolley  or  I-beam  traveler,  the  track  for  which  is  sus- 
pended from  the  ceiling  of  the  second  floor  and  extends  through  an 
opening  in  the  end  wall  similar  to  a  hay-trolley  on  a  barn.  The 
hoisting  is  done  by  an  electric  motor  which  is  mounted  directly  on 
the  trolley  traveler. 

A  novel  method  is  used  for  handling  the  air  and  water  for 
washing.  Small  motor-driven  centrifugal  wash  pumps  and  rotary 
air  pumps  in  duplicate  are  located  in  the  basement  and  these 
deliver  into  the  combined  air  and  wash-water  tanks  shown  in 
Fig.  36.  This  is  really  a  gasometer,  the  lower  tank  holding  the 
wash  water  and  serving  to  seal  the  upper  inverted  air  tank,  which 
rises  and  falls  as  the  volume  of  air  contained  varies.  This  enables 
small  wash  and  air  pumps  to  be  used,  running  about  50  per  cent 
of  the  time,  and  allows  the  electric  generating  plant  to  be  kept 
down  to  a  reasonable  size.  These  pumps  shut  off  automatically 
when  the  tank  fills  up,  and  start  after  the  water  and  air  levels  drop 
a  certain  amount. 

As  it  is  expensive  to  pump  water  up  to  the  plant,  the  dirty  wash 
water  is  collected  in  a  settling  basin,  and  after  the  silt  settles  out  is 
repumped  into  the  sedimentation  basins,  by  automatically  con- 
trolled centrifugal  pumps. 

The  generating  plant  is  of  30  kilowatt  capacity,  gas-engine 
driven.  The  heating  plant  is  of  the  usual  steam-boiler  type. 

This  plant  was  installed  by  the  Pennsylvania  Water  Co., 
W.  C.  Hawley,  chief  engineer  and  superintendent.  Mr.  J.  N. 
Chester,  of  Chester  &  Fleming,  Pittsburgh,  was  consulting  en- 
gineer. The  Pittsburgh  Filter  Manufacturing  Co.  furnished  and 
installed  the  equipment. 

The  Filtration  and  Softening  Plant  at  Columbus,  Ohio.*  The 
Columbus  filtration  plant  is  an  excellent  example  of  an  in- 

*  Engineering  Record,  February  24,  1906. 


TYPES    OF    PURIFICATION    PLANTS 


75 


stallation  designed  to  soften  as  well  as  to  filter  the  water.  The 
source  of  supply  is  the  Scioto  River,  which  drains  a  region  under- 
lain with  dolomite  (mixed  calcium  and  magnesium  carbonate),  and 
consequently  the  water  is  quite  hard,  the  total  hardness  being 


Courtesy  Pittsburgh  Filter  Manufacturing  Company. 

FIG.  36. — Wilkinsburg  -Filtration  Plant,   Combined  Air  and  Wash-Water 

Tank. 

about  250  parts  per  million,  and  the  incrustants  averaging  about 
100  parts  per  million.  The  treatment  given  the  water  reduces 
the  total  hardness  to  80  and  the  incrustants  to  about  40  parts  per 
million.  The  capacity  of  the  plant  is  30,000,000  gallons  per  day. 
The  water  is  treated  with  lime  to  precipitate  the  bicarbonates  of 
calcium  and  magnesium,  then  with  soda  ash  to  remove  the  in- 
crustants, and  finally  alum  is  added  as  a  coagulant,  although 


76  WATER    PURIFICATION    PLANTS 

an  effort  is  made  to  utilize  the  gelatinous  magnesium  hydroxid 
formed  in  the  softening  process  for  this  purpose. 

The  general  layout  of  the  plant  is  shown  in  Fig.  37,  referring 
to  which  it  will  be  seen  that  the  water  enters  a  weir  basin  (which 
forms  the  first  floor  of  the  head  house) ,  through  a  48-inch  cast-iron 
main,  passing  through  a  Venturi  meter  immediately  before  entering 
this  basin.  Besides  recording  the  rate  of  pumpage  of  the  raw 
water,  this  meter  also  controls  the  rate  of  discharge  of  the  coagulant 
solutions,  varying  this  in  proper  ratio  to  the  raw-water  pumpage. 

Along  the  sides  of  the  weir  basin  are  adjustable  weirs,  of  which 
there  are  three  sets  of  two  each,  for  diverting  certain  proportions 
of  the  raw  water  to  lime  saturators,  soda  trough,  and  mixing  tanks. 
The  plant  was  designed  so  that  a  maximum  of  25  per  cent  of  the 
raw  water  passed  over  the  weirs  to  the  lime  saturators,  a  similar 
amount  over  the  soda  weir,  and  the  remaining  50  per  cent  passed 
over  the  weirs  into  the  mixing  tanks.  An  additional  weir  was 
provided  for  feeding  untreated  water  to  the  effluent  of  the  settling 
basins,  to  eliminate  any  caustic  alkalinity  of  the  settled  water  due 
to  overtreatment  with  lime;  and  an  overflow  weir,  slightly  higher 
than  the  rest  and  leading  to  the  settling  basins,  takes  care  of  undue 
fluctuations  in  the  raw-water  pumpage. 

To  the  portion  passing  over  the  lime  weirs,  milk  of  lime  is 
supplied  by  means  of  a  perforated  pipe,  after  which  the  water 
passes  into  the  six  lime  saturators  by  means  of  a  central  flume 
with  a  branch  pipe  into  each  saturator.  Within  the  saturator 
tank  each  pipe  divides  into  four  branches,  which  distribute  the  lime 
and  water  evenly  over  the  bottom  of  the  tank.  The  water  rises 
slowly  in  the  tank,  being  constantly  stirred  by  revolving  paddles 
(four  sets  per  saturator),  and  overflows  into  a  central  flume  be- 
tween the  two  rows  of  saturators  and  above  the  entrance  flume. 
Thus  the  water  and  lime  are  intimately  mixed,  giving  a  saturated 
solution  of  lime  water  (about  60  grains  per  gallon).  The  lime- 
saturated  water  flows  through  the  flume  and  a  cast-iron  pipe  be- 
neath the  weir  basin  and  enters  the  mixing  tanks  together  with  the 
main  body  of  water. 

The  purpose  of  the  mixing  tanks  is  to  bring  about  a  thorough 

mixture    of    the    water    with    the    softening    reagents,    thereby 

'  greatly   facilitating   the   reactions.     These   tanks   have    a   total 

capacity  of  nearly  1,000,000  gallons,  so  that  the  water  requires 

almost  an  hour  to  pass  through  them.     They  are  two  in  number, 


8  "Vitrified  Drain 


Wash  Water  \  Manhole       Slope  I  in  200 
Tank  I   e"<3.L  Pipe  Pressure  Supply 


Engineering  Record,  February  24, 1906. 


FIG.  37. — Columbus  F 


•i                                                   N 

L-__ 

/ 

i 

Paving 
Concrete  Pathway  1 

Roadway  EL  64.0 

Basin                                          >, 

in                         Tx 

.;  H                                    Toe  of  Slope  El.42.0          ^  J 

Lower  Limit  of  Paving  EL55.0 


ftbion  Plant,  General  Plan. 


TYPES    OF    PURIFICATION    PLANTS 


77 


78 


WATER    PURIFICATION    PLANTS 


arranged  on  either  side  of  a  central  gallery,  which  contains  the  con- 
duit for  carrying  the  mixed  water  to  the  settling  basins,  the  flume 
for  introducing  the  soda  ash  (as  will  be  explained  presently),  and 
the  mixing  tank  blowoffs  for  drainage  and  cleaning.  The  mixing 
tanks  are  fitted  with  vertical  baffles  spaced  3  feet  on  centers, 
causing  the  water  to  take  a  circuitous  course,  passing  over  one 


Pressure 
Pipe 


DIVIDING  MAIN  WALL  OF  SETTLING  BASIN 


Engineering  Record,  February  24,  1906. 

FIG.  39. — Columbus  Filtration  Plant. 

baffle  and  under  the  next.  Sluice  gates  into  the  receiving  conduit 
are  provided  at  intermediate  points,  so  that  a  shorter  period  of 
mixture  can  be  obtained  if  desired. 

The  soda  ash  is  introduced  into  its  quota  of  water  as  this  is 
passing  over  the  soda  weirs,  and  travels  through  a  flume  at  the  top 
of  the  gallery  between  the  mixing  tanks,  entering  these  at  a  point 
60  feet  from  the  weir  basin,  via  an  overflow  weir  extending  across 
both  tanks.  The  construction  of  the  mixing  tanks  is  shown  by 
Fig.  38. 

The  treated  and  thoroughly  mixed  water  passes  on  to  the 


TYPES    OF    PURIFICATION    PLANTS  79 

settling  basins,  which  have  a  capacity  of  15,000,000  gallons,  or  a 
period  (nominally)  of  12  hours.  Through  the  settling  basins  ex- 
tends a  dividing  wall,  which  is  cored  out  as  shown  by  Fig.  39  to 
form  three  flumes  or  gullets,  the  upper  carrying  the  softened  water 
to  the  basins,  the  middle  carrying  the  settled  water  from  the 
basins  to  the  filters,  and  the  lower  being  used  to  drain  the  basins 
and  containing  the  blowoff  valves.  The  upper  level  of  this 
wall  serves  as  a  gate-house,  containing  the  sluices  controlling  the 
admittance  of  water  to  and  withdrawal  from  the  basins,  and  is 
enclosed  in  a  brick  superstructure.  Laterally  the  basins  are 
further  subdivided  by  walls  so  as  to  form,  in  all,  six  compartments. 
Each  compartment  has  a  vertical  baffle  through  the  middle,  ex- 
tending from  the  main  dividing  wall  to  within  60  feet  of  opposite 
end,  compelling  the  water  to  make  a  complete  circuit  of  the  com- 
partment, i.e.,  leaving  the  softened-water  flume  it  would  travel 
outward  from  the  main  dividing  wall  laterally  in  both  directions 
to  the  far  end  of  the  baffles,  around  these,  and  then  back  to  the 
dividing  wall,  repeating  the  process  for  each  compartment.  The 
water  in  each  half  of  the  basin  would,  therefore,  make  six  complete 
passes  across  the  basin  before  reaching  the  settled-water  conduit  at 
the  outer  end  of  the  dividing  wall.  It  is  also  possible  to  distribute 
the  water  so  that  each  compartment  of  the  basin  takes  its  quota 
of  the  water,  making  essentially  six  smaller  settling  basins,  each 
receiving  one-sixth  of  the  water.  This  would  reduce  the  velocity 
through  the  basins  to  one-third  of  the  normal.  Any  compart- 
ment can  be  shut  down,  drained,  and  flushed  by  pressure  hoses. 

After  passing  through  the  settling  basins,  the  water  is  carried 
to  the  filters  through  the  settled-water  flume.  There  are  ten 
filter  units,  each  of  3,000,000  gallons  per  day  capacity.  They 
offer  no  novel  points  not  already  described.  Fig.  40  gives  sections 
through  one  of  the  filters  and  the  pipe  gallery.  The  settled  water 
enters  the  gallery  by  means  of  a  48-inch  "  raw-water  "  pipe,  with 
20-inch  branches  entering  the  units  at  the  central  gutter.  The 
water  is  filtered  through  30  inches  of  sand  (effective  size,  0.4  mm., 
uniformity  coefficient,  1.5),  and  through  a  layer  of  graded  gravel 
(from  /is  to  1  inch  in  size).  A  detail  of  the  strainer  system  is 
shown  by  Fig.  42.  The  ridges  shown  are  8%  inches  on  centers, 
and  the  brass  strainer  plates  in  the  valleys  are  similarly  spaced. 
The  filtered  water  is  collected  by  a  pipe  manifold  and  passes  via 
a  rate  controller  and  effluent  pipe  to  the  clear-water  reservoir. 


80 


WATER    PURIFICATION    PLANTS 


30  Drain 


48  Effluent 


Engineering  Record,  February  24,  1906.  FlG.  41. — Columbus  Filtration  1 


EL  61.60. 


fete 

Controller  Ste 

'Wash       10*Air 
Wat€r  Air 

Wash  Water 

»  {1 

Raw  Water  Drain 
Filtered  Water- 
Controller. 

»  Filtered  Water 


'Wheel  Stand 

•Operating  Table- 

Float  Tnbea 


SECTION   C-D 


EL  61.5X 


Operating  Table -^ 


SECTION   E-F 

.    Details  of  Piping  in  Filters  and  Pipe  Gallery. 


TYPES    OF    PURIFICATION    PLANTS 


81 


Wash  water  is  supplied  from  a  reinforced  concrete  tank  and 
delivered  to  the  niters  by  a  24-inch  line  passing  through  the  pipe 
gallery  with  20-inch  branches  into  each  unit.  It  is  distributed 
throughout  the  filter  unit  by  means  of  the  strainer  system.  After 
rising  upward  through  and  cleansing  the  sand,  it  is  removed  by 


DETAILS  OF  STRAINER 
Engineering  Record,  February  24,  1 906. 

FIG.  42. — Columbus  Filtration  Plant. 

six  lateral  gutters  in  each  half  of  the  filter,  leading  into  the  central 
gutter,  and  is  thence  carried  away  by  a  30-inch  drain  in  the  filter 
gallery.  The  plant  is  designed  to  give  a  rate  of  wash  of  8  gallons 
per  square  foot  per  minute. 

In  addition  to  water,  air  is  used  for  agitation  before  or  during 
washing,  and  for  this  purpose  a  system  of  air  pipes  and  manifold  is 
provided.  There  is  a  12-inch  air-supply  line  in  the  gallery,  with  10- 
inch  branches  to  each  filter.  These  branches  are  hung  along  the 
central  gutter,  and  outlets  in  the  bottom  connect  with  lateral 
pipes  supported  on  the  concrete  ridges  which  hold  down  the 
gravel.  These  laterals  are  1  inch  in  diameter,  made  of  brass  and 
spaced  8J£  inches  apart.  They  are  drilled  on  the  bottom  with 
3/g-inch  holes,  8%  inches  center  to  center.  The  air  system  is  de- 
signed for  a  maximum  rate  of  3  cubic  feet  of  air  per  square  foot  per 
minute. 

All  valves  in  the  operating  gallery  are  hydraulically  controlled, 


82 


WATER    PURIFICATION    PLANTS 


TYPES    OF    PURIFICATION    PLANTS 


83 


the  levers  for  each  unit  being  grouped  on  a  marble  table,  which 
also  contains  the  loss-of-head  gage.  Each  filter  is  further  equipped 
with  a  small  pump  and  motor,  which  draws  water  from  the  ef- 


Courtesy  Charles  P.  Hoover,  Chemist  in  Charge. 

FIG.  44. — Columbus  Filtration  Plant.     Raising  Lime  Bags  by  Continuous 

Elevator. 

fluent  pipe  and  discharges  it  into  a  small  bowl  on  the  operating 
table,  so  that  a  sample  of  filtered  water  from  any  unit  can  be 
readily  obtained. 


84  WATER    PURIFICATION    PLANTS 

A  one-story  superstructure  entirely  covers  the  top  of  the 
mixing  tanks  and  serves  as  a  storage  house  for  lime,  soda  ash,  and 
alum.  The  chemicals  are  received  in  carload  lots,  generally  in 
bags,  there  being  a  railroad  siding  on  each  side  of  the  storage 
house,  which  has  unloading  platforms  and  side  doors  similar  to  a 
freight  station.  The  capacity  of  the  storage  house  is  900  tons, 
or  about  20  carloads.  An  apron  conveyor,  running  centrally  the 
entire  length  of  the  storage  house,  and  driven  by  an  18-horse-power 
motor,  serves  for  carrying  the  bags  of  chemicals  to  the  third  floor  of 
the  head  house,  where  the  solutions  are  made  up. 

The  second  floor  of  the  head  house  is  almost  completely  filled 
by  the  chemical-solution  tanks,  of  which  there  are  nine,  three  each 
for  soda,  coagulant  (alum  or  ferrous  sulphate),  and  lime.  The 
tanks  are  of  reinforced  concrete,  circular,  12  feet  6  inches  in  dia- 
meter and  11  feet  5  inches  deep.  The  coagulant  and  soda  solu- 
tions are  kept  uniform  by  agitation  with  compressed  air,  an  air 
grid  of  brass  piping  in  each  tank  distributing  the  air  uniformly. 
In  the  lime  tanks,  revolving  paddles  on  a  centrally  mounted  ver- 
tical shaft  serve  the  same  purpose.  The  tanks  are  provided  with 
the  customary  piping  for  carrying  the  solutions  to  the  orifice  boxes, 
and  for  draining,  and  each  tank  is  equipped  with  a  float  gage  for 
recording  the  depth  of  solution. 

The  tops  of  the  solution  tanks  support  the  third  floor  of  the 
head  house.  Here  are  located  the  devices  for  making  up  the 
chemical  solutions.  The  apron  conveyor  enters  through  the  wall 
of  this  building  adjacent  to  the  storage  house  and  traverses  it 
centrally  for  about  two-thirds  the  length,  at  which  point  the  head 
pulley  of  the  conveyor  is  located.  Bags  of  chemicals,  if  not 
removed  previously,  are  therefore  dumped  automatically  at  this 
point.  As  the  amount  of  lime  used  exceeds  that  of  alum  and 
soda,  it  is  delivered  in  this  way,  and  the  slaking  tanks  are  located 
conveniently  to  the  end  of  the  conveyor.  They  are  three  in  num- 
ber, 6  feet  in  diameter  and  2  feet  8  inches  deep,  built  of  rein- 
forced concrete.  Hot  water  is  used  in  slaking,  and  the  lime  and 
water  are  stirred  during  the  process  by  motor-driven  vertical 
rakes.  The  slaked  lime  is  discharged  into  the  lime-solution  tanks 
already  described.  There  are  two  dissolving  tanks  each,  for 
coagulant  and  soda  ash,  conveniently  located  along  the  sides  of  the 
conveyor.  These  tanks  are  of  concrete,  rectangular  in  plan, 
5  feet  long,  3  feet  wide,  and  2  feet  8  inches  deep.  The  material 


TYPES   OF   PURIFICATION   PLANTS  85 

to  be  dissolved  is  placed  on  a  screen  about  3  inches  above  the 
bottom  of  the  tank,  and  water  (which  may  be  heated)  is  passed 
upward  through  it,  overflowing  a  weir  and  passing  into  the  solu- 
tion tanks.  Scales  for  weighing  are  provided,  and  a  chute  is 
located  at  one  end  of  the  building  by  means  of  which  empty 
sacks  are  returned  to  the  storage  room,  where  they  are  packed  for 
shipment  to  the  chemical-supply  company. 

The  chemical  solutions  are  fed  to  the  raw  water  automatically 
in  proportion  to  its  amount  by  orifice  boxes  controlled  through 
the  Venturi  meter  in  the  raw-water  main. 

The  plant  contains  the  usual  offices,  bacteriological  and  chem- 
ical laboratories,  a  locker  room,  lavatory,  and  storeroom. 

Soon  after  commencing  operation  the  method  of  handling  lime 
was  found  to  be  unsatisfactory.  The  bags  of  lime  varied  as  much 
as  15  pounds  from  the  standard  weight,  and  on  storage  they  air- 
slaked  and  broke  open.  Thereafter  the  lime  was  bought  in  bulk 
and  sacked  at  the  plant,  which  proved  a  disagreeable  and  un- 
satisfactory method.  To  overcome  these  difficulties,  a  system  of 
conveyors  and  automatic  scales  was  installed  and  put  into  service 
in  1913.* 

Referring  to  Fig.  45,  it  will  be  seen  that  a  large  overhead 
storage  bin,  having  a  capacity  of  220  tons,  was  built  over  one  of  the 
sidings  adjacent  to  the  head  house.  The  lime,  being  received  in 
bulk,  in  carload  lots,  is  fed  into  a  hopper  by  means  of  a  power 
shovel  operated  by  a  man  in  the  car.  From  this  hopper  the  lime 
is  fed  to  a  bucket  elevator  by  a  screw  feeder  and  lifted  into  the 
bin.  To  supply  the  solution  tanks,  the  lime  in  the  storage  bin  is 
fed  to  the  elevator  through  a  chute  from  the  bin  bottom  and  is 
lifted  to  an  overhead  screw  conveyor,  which  carries  it  to  any  of 
three  smaller  hoppers  suspended  over  the  three  lime-slaking  tanks. 
Each  of  these  hoppers  feeds  into  an  automatic  weighing  device, 
electrically  controlled,  which  weighs  out  a  predetermined  quantity 
of  lime  at  regular  intervals  into  the  slaking  tanks,  whence  the 
lime  solution  travels  through  the  solution  tank  and  orifice  box 
to  the  raw  water  as  already  described. 

The  weighing  device  consists  of  an  equal-armed  scale  (like 
a  chemical  balance  in  principle),  to  one  arm  of  which  the  desired 
weight  is  attached,  while  the  other  suspends  a  receptacle  to  receive 

*  Annual  Report,  Division  of  Water,  Columbus,  O.,  1913. 


86 


WATER    PURIFICATION    PLANTS 


TYPES    OF    PURIFICATION    PLANTS 


87 


the  lime  from  the  hopper  above.  The  tilting  of  the  beam,  when  the 
proper  amount  is  weighed  out,  automatically  closes  a  gate  in  the 
bottom  of  the  hopper.  The  charge  is  dumped  into  the  slaking 
tank  through  an  opening  in  the  bottom  of  the  receptacle,  the 
gate  to  which  is  opened  at  the  proper  time  by  an  electromagnet. 


ELECTRIC  CONTROL  APPARATUS  FOR  THREE  RICHARDSON  AUTOMATIC  LIME  SCALES 
SUPPLIED  BY  THE  RICHARDSON  SCALE  CO.,  PASSAIC.N.J-,  CHICAGO  AND  NEW  YORK,, 


FIG.  46. — Columbus  Filtration  Plant.     Timing  Device  for  Automatic  Scales. 

The  electric  circuit  controlling  the  dumping  is  closed  by  the  clock 
device  shown  in  Fig.  46.  A  clockwork  gives  a  uniform  rotative 
movement  to  a  circular  disk  with  contact  points  on  its  periphery. 
Every  time  a  contact  is  made,  the  electric  circuit  actuating  the 
magnet  in  the  weighing  device  is  closed,  and  a  charge  of  lime  is 


WATER    PURIFICATION    PLANTS 


dumped.  Different  disks  are  used  to  give  any  desired  interval 
between  contacts.  A  number  of  these  are  shown  in  the  right  and 
left  hand  corners  of  the  case  containing  the  apparatus.  Switches 
are  provided  to  throw  any  of  the  three  weighing  devices  into 


Engineering  Record,  July  23, 1910.. 

FIG.  47. — Iowa  City  Iron  Removal  Plant.     General  Plan  of  Purification 

Works. 

operation  and  electric  lights  in  series  with  the  circuits  indicate 
that  these  are  unbroken  by  lighting  up  with  each  discharge. 

The  original  design  and  construction  was  carried  on  under 
direction  of  Messrs.  Julian  Griggs  and   Henry  Maetzel,  succes- 


TYPES    OF    PURIFICATION    PLANTS 


89 


.1 


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3 

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'% 

90  WATER    PURIFICATION    PLANTS 

sively  chief  engineers  of  the  Board  of  Public  Service.  Mr.  John 
H.  Gregory  was  engineer  in  charge  and  Messrs.  Rudolph  Bering 
and  George  W.  Fuller  were  consulting  engineers.  The  later  im- 
provements were  carried  out  by  Messrs.  Charles  P.  Hoover, 
chemist  in  charge,  and  C.  J.  Clarke,  engineer  of  the  water-works 
department. 

The  Iron-Removal  Plant  at  Iowa  City,  la.*  The  mechanical 
filter  plant  requires  no  especial  adaptation  in  order  to  remove  iron 
successfully.  If  in  the  bicarbonate  form,  the  addition  of  lime, 
followed  by  sedimentation  of  sufficient  duration  to  allow  of  com- 
plete reaction  between  the  lime  and  bicarbonates,  and  filtration 
to  remove  the  precipitate,  will  eliminate  the  iron  very  readily. 
Sometimes  a  coagulant  is  added  to  hasten  precipitation.  Such  a 
plant  is  in  successful  operation  at  Iowa  City,  la.  The  water 
supply  is  obtained  from  galleries  in  the  bed  of  the  Iowa  River, 
and  contains  from  3.5  to  4.3  parts  per  million  of  iron. 

The  mechanical  filter  plant  consists  of  lime-dosing  apparatus, 
settling  basins,  and  filters  of  2,000,000  gallons  per  day  capacity. 
The  water  is  raised  from  the  galleries  to  the  settling  basins  by 
centrifugal  pumps,  steam  driven.  Lime  solution  is  applied  near 
the  point  of  entrance  into  the  basins.  The  basins,  two  in  number, 
are  of  250,000  gallons  capacity.  The  water  takes  a  circuitous 
route  through  these  and  enters  a  flume  extending  along  the  rear  of 
the  filters,  as  shown  by  Fig.  47.  In  this  case,  as  in  the  Torresdale 
plant,  the  settled  water  enters  the  filters  at  the  rear  through 
valved  branches  from  the  flume.  While  this  simplifies  con- 
struction, it  has  the  opposite  effect  on  operation.  Each  filter 
contains  one  cast-iron  wash  trough  through  the  center,  by  way  of 
which  the  settled  water  is  also  introduced  and  distributed.  The 
filtering  material  consists  of  28  inches  of  sand  of  the  usual  size, 
supported  on  12  inches  of  graded  gravel.  The  collector  manifold 
consists  of  a  single  6-inch  cast-iron  header  extending  longitudinally 
through  the  center  of  the  filter  with  lJ/2-inch  wrought-iron  laterals 
on  either  side,  spaced  6  inches  center  to  center.  Brass  strainer 
heads  are  tapped  into  these  laterals,  5/i6  inches  on  centers. 

The  filters  are  washed  in  the  usual  way,  both  air  and  water 
being  used.  Wash  water  is  supplied  by  an  8-inch  centrifugal 
pump  at  the  rate  of  7.5  gallons  per  square  foot  per  minute,  the 
dirty  wash  water  overflowing  into  the  central  trough  and  being 

*  Engineering  Record,  July  23,  1910 


TYPES    OF    PURIFICATION    PLANTS 


91 


led  into  a  sewer.     Air  is  used  in  the  customary  manner,  being  dis- 
tributed through  the  same  manifold  as  the  wash  water. 

Two  lime-solution  tanks,  12  feet  in  diameter  and  10  feet  6 
inches  deep,  are  located  along  one  end  of  the  settling  basins.  The 
lime  is  slaked  in  a  concrete  box,  3  feet  wide,  9  feet  long,  and  2  feet 
deep,  placed  on  the  floor  above  the  solution  tanks,  and  is  discharged 


Index  Wheel 


Orifice 


Engineering  Record,  July  23, 1910. 

FIG.  49. — Iowa  City  Iron-Removal  Plant. 


Lime-Solution  Orifice. 


into  the  latter  through  sluice  gates  at  both  ends  of  the  box.  The 
lime  solution  is  kept  uniform  in  strength  by  means  of  revolving 
paddles  in  the  solution  tanks.  Pipes  from  these  tanks  lead  to  two 
lJ/2-ineh  bronze  centrifugal  pumps,  which  raise  the  solution  to  an 
elevated  orifice  box,  through  which  it  is  discharged  into  the  raw- 
water  main.  Fig.  49  shows  a  detail  of  the  orifice  box.  The  orifice 
consists  of  an  annular  slot  in  a  rubber  disk,  the  opening  of  which 
can  be  varied  by  means  of  a  revolving  sector  turned  by  a  vertical 
shaft.  An  index  wheel  at  the  top  of  the  shaft  indicates  the  rel- 
ative size  of  the  orifice.  A  constant  head  is  maintained  by  means 
of  an  overflow  weir  discharging  back  into  the  solution  tanks.  A 
clear-water  basin  is  located  below  the  filters. 

The  plant  is  of  reinforced  concrete  construction  with  brick 
superstructure.  As  it  was  built  for  a  special  purpose  and  at  a 
minimum  cost,  it  does  not  possess  the  flexibility  and  ease  of  opera- 
tion desirable  in  the  average  plant.  This  plant  was  designed  and 
built  by  the  New  York  Continental  Jewell  Filtration  Company. 


CHAPTER  III 

PHYSICAL  AND  CHEMICAL  TESTS 

TESTS  must  be  made  in  connection  with  water  purification  in 
order  to  ascertain  those  qualities  of  the  raw  water  affecting  its 
treatment,  to  measure  the  improvement  effected  by  purification, 
and  to  make  sure  that  the  filtrate  is  up  to  the  standard  of  purity. 

It  is  not  necessary  to  make  a  complete  analysis  of  the  water, 
in  fact,  it  is  not  desirable,  as  to  do  so  would  occupy  much  valuable 
time,  which  could  be  better  employed  outside  of  the  laboratory. 
It  is  of  greater  importance  that  the  determinations  herein  out- 
lined be  made  with  sufficient  frequency  to  include  all  possible 
variations  in  the  condition  of  the  raw  water,  in  general  not  less 
than  once  a  day. 

The  usual  tests  to  be  made  are  as  follows: 

In  the  Raw  Water:  In  the  Filtrate: 
Taste  and  odor  Taste  and  odor 

Turbidity  Turbidity 

Color  Color 

Alkalinity  or  acidity  Alkalinity 

Free  carbonic  acid  (CO2)  CO2 

Iron  Free  alum  or  ferrous  sulphate 

Bacterial  count  at  20°  Cent.          Iron 

Bacterial  count  at  37°  Cent.         Bacterial  count  at  20°  Cent. 
Coli  determinations  Bacterial  count  at  37°  Cent. 

Coli  determinations 

Of  these,  color  may  be  omitted  in  waters  where  this  quality  is  of 
small  moment,  and  iron  except  in  the  case  of  waters  containing  an 
appreciable  amount.  The  remaining  tests  are  necessary  in  order 
to  keep  well  informed  on  the  condition  of  the  raw  and  filtered 
water. 

In  carrying  out  the  following  tests,  great  care  should  be  ob- 
served, in  order  to  insure  accurate  results.  The  apparatus  used 
should  be  clean,  and  immediately  before  use  should  be  wiped  out 
with  a  clean  cloth  and  then  rinsed  out  with  distilled  water  of 

93 


94 


WATER    PURIFICATION    PLANTS 


Mouth  Piece 


known  purity.  This  is  best  accomplished  by  means  of  a  wash 
bottle,  Fig.  50.  This  consists  of  a  liter  flask,  with  rubber  stopper 
perforated  for  two  glass  tubes  as  shown.  By  blowing  into  the 
mouthpiece,  a  fine  stream  of  distilled  water  can  be  directed  on 
apparatus  requiring  to  be  rinsed.  Glass  tubing  for  making  this 
and  other  apparatus  can  be  cheaply  bought  and  bent  to  the  de- 
sired shape  by  heating  to  redness  in  an  ordinary  gas  flame.  The 

tubing  can  be  cut  with  a  small  tri- 
angular file,  by  nicking  and  then 
breaking  it,  the  cut  ends  being 
rounded  in  the  gas  flame.  Ap- 
paratus should  be  thoroughly 
rinsed  and  dried  after  use.  Oc- 
casionally it  should  be  cleaned 
with  the  solution  described  in 
Chapter  IV,  being  thoroughly 
rinsed  afterward  to  remove  all  traces 
of  fluid. 

Care  must  be  used  in  measur- 
ing samples  to  obtain  the  exact 
amount  required,  as  well  as  in  read- 
ing the  burettes  and  observing  the 
end  point  in  tests  involving  indi- 
cators. Needless  to  say,  samples 
should  be  collected  in  clean  bottles, 
and  before  testing  it  is  well  to  rinse 
the  mouth  of  the  sample  bottle  by 
pouring  out  and  wasting  some  of 
the  water  contained.  If  distilled 

water  is  not  available,  the  apparatus  should  be  washed  out  be- 
fore use  with  some  of  the  water  to  be  tested. 

A  supply  of  distilled  water  is  very  desirable  for  laboratory  use. 
The  bottled  "  distilled  "  water  on  the  market  is  often  untrust- 
worthy and  should  not  be  accepted  as  reliable  until  proved  by  the 
tests  given  in  this  chapter,  especially  those  for  C02,  alkalinity,  and 
iron,  which  should  all  give  negative  results.  More  thorough  tests 
are  given  in  Appendix  B.  If  possible  the  water  should  be  distilled 
in  the  laboratory.  The  apparatus  required  is  shown  in  Fig.  51. 
The  water  to  be  distilled  is  placed  in  the  boiler  (a),  generally  made 
of  copper,  tin-lined,  and  is  evaporated  by  means  of  a  Bunsen  burner 


FIG.  50.— Wash  Bottle. 


PHYSICAL   AND    CHEMICAL   TESTS 


95 


Condenser 


From  Tap 


FIG.  51.— Water  Still. 


96 


WATER   PURIFICATION    PLANTS 


Glass  Tube 


Loose  Stopper 


/      \ 


Hose 


Pinch  Cock  QD= 


Carboy 


placed  below  the  boiler.  The  steam  passes  off  through  the  block 
tin  tube  into  a  "  worm  "  or  condenser  of  the  same  material,  im- 
mersed in  a  tank  of  cold  water,  causing  it  to  condense.  The 
distilled  water  is  collected  in  the  bottle  (6).  •  A  constant  supply  of 
cool  water  is  kept  circulating  about  the  worm  by  means  of  a  hose 

connection  from  the  tap,  and 
a  waste  overflow,  generally 
carried  by  a  hose  to  the  sink. 
The  first  portion  of  the  dis- 
tillate caught  by  the  bottle 
(6)  should  be  used  to  rinse 
out  same  and  then  be  wasted. 
Distilled  water  greedily  ab- 
sorbs CO2  and  oxygen  from 
the  air,  and,  if  desired  to 
be  free  of  these,  should  be 
freshly  boiled.  The  labora- 
tory supply  of  distilled  water 
is  conveniently  kept  in  the 
container  shown  by  Fig.  52. 
It  consists  of  a  large  glass 
carboy,  loosely  corked,  with 

a  siphon  made  of  glass  and  rubber  tubing.  The  water  can  be 
pulled  over  into  the  siphon  by  suction  and  will  then  continue 
to  flow  whenever  the  pinch-cock  is  opened  until  the  carboy  is 
empty. 

It  is  suggested  that  those  inexperienced  in  making  chemical 
preparations  obtain  the  reagents  and  standard  solutions  required 
in  the  following  tests  from  a  competent  chemist  or  chemical 
supply  house.  Those  wishing  to  prepare  their  own  standard 
solutions  will  find  directions  in  Appendix  B. 

Extreme  care  should  be  used  in  handling  and  preserving 
standard  solutions.  They  should  be  kept  in  hard  glass,  glass- 
stoppered  bottles,  except  sodium  carbonate,  the  container  for 
which  is  preferably  rubber-stoppered.  The  bottles  should  be  kept 
closed  at  all  times  to  prevent  the  entrance  of  impurities  or  evapora- 
tion of  the  solution.  The  stoppers  when  removed  should  never 
be  laid  on  their  sides,  nor  should  the  mouth  of  the  bottle  be 
carelessly  handled.  Before  opening,  the  mouth  and  neck  of  the 
bottle  should  be  wiped  free  of  dust  with  a  clean  dry  cloth.  In 


FIG.  52.— Distilled-Water  Container. 


PHYSICAL   AND    CHEMICAL   TESTS  97 

transferring  solutions  to  bottles  or  burettes,  the  latter  should  be 
perfectly  clean  and  dry.  A  small  amount  of  the  solution  should 
then  be  poured  into  the  bottle  or  burette,  and  used  to  rinse  the 
same  thoroughly,  being  then  poured  out.  After  this  preliminary 
rinsing  the  bottle  or  burette  may  be  filled  with  the  solution. 
Burettes  should  be  fitted  with  a  small  glass  cap,  or  else  corked, 
when  not  in  use,  to  prevent  evaporation.  It  is  not  advisable  to 
keep  a  large  stock  of  standard  solutions  on  hand,  as  these  de- 
teriorate, it  being  preferable  to  make  or  have  made  new  solutions 
at  intervals  of  a  few  months.  Where  large  amounts  of  solutions 
are  used,  a  standard  may  be  prepared  with  especial  care,  and  kept 
for  comparative  purposes,  the  solutions  used  being  made  up  to  the 
required  strength  by  titration  with  this  standard.  A  ^  solution 
of  sulphuric  acid  is  well  adapted  for  this  purpose  and  will  keep  a 
long  time.  Then  to  prepare  a  ^  solution  of  sodium  carbonate 
dissolve  the  approximate  amount  required  (see  Appendix  B)  in  a 
liter  of  double-distilled  water  and  titrate  10  cc.  of  this  solution 
with  the  standard  acid,  using  erythrosin  or  methyl  orange  as  an 
indicator.  The  sodium  carbonate  solution  should  be  made  a 
little  strong,  and  then  diluted  down  with  distilled  water  until 
10  cc.  of  the  standard  acid  will  exactly  neutralize  10  cc.  of  the 
sodium  carbonate  solution.  An  acid  solution  for  general  use  can 
now  be  made,  using  the  sodium  carbonate  just  prepared  as  a 
standard  of  comparison.  (In  preparing  acid  solutions,  or  in 
diluting  strong  acids,  the  acid  should  always  be  poured  into  the 
water;  if  this  operation  is  reversed  the  acid  will  sputter  and  fly 
about  and  may  cause  painful  and  dangerous  burns.)  To  prepare 
solutions  of  other  concentrations,  it  is  only  necessary  to  vary  the 
ratio  of  standard  solution  used  in  titration.  Thus  for  a  ^  solu- 
tion of  sodium  carbonate,  a  sample  of  10  cc.  should  require  50  cc. 
of  the  ^  sulphuric  acid  to  neutralize  it;  for  a  ^  solution  |rj  X  10 
or  22.7  cc.  of  the  sulphuric  acid  would  be  required. 

The  metric  system  of  measurement  is  used  in  chemical  and 
bacterial  work.  Lengths  are  measured  in  meters,  decimeters 
(1/10  meter),  centimeters  (1/100  meter),  and  millimeters  (1/1000 
meter).  The  symbols  for  these  units  are  "  m.,"  "  cm.,"  and  "  mm." 
respectively.  Volumes  are  measured  in  cubes  of  the  linear  units, 
thus  cubic  centimeters  (abbreviation  "  cc."),  and  cubic  decimeters 
are  commonly  used,  the  latter  being  the  unit  of  liquid  measure 
and  being  called  the  "liter"  (abbreviation  "  L").  It  follows 


98  WATER    PURIFICATION    PLANTS 

that  a  liter  equals  1000  cc.  Units  of  weight  are  the  gram,  which  is 
the  weight  of  1  cc.  of  water  under  standard  conditions,  the  multiples 
being  the  "  kilogram  "  (1000  grams)  and  the  milligram  (1/1000 
gram).  The  abbreviations  used  are  respectively,  "  gm.,"  "  kgm.," 
"  mgm."  The  following  table  shows  the  relation  between  units 
of  the  English  and  metric  systems. 

TABLE 

1  inch  =     2.54  centimeters 

1  foot  =  30.48  centimeters 

1  yard  =     0.9144  meters 

1  pound  =     0.454  kilograms 

1  ounce  =  28.35  grams 

1  grain  =  64.80  milligrams 

1  pint  =     0.568  liters 

The  strength  of  standard  solutions  is  given  as  normal  (abbre- 
viated "  N."),  or  fractions  thereof,  thus  one-fiftieth  normal  (^), 
one-tenth  normal  (^).  The  meaning  of  these  terms  is  beyond 
the  scope  of  this  book,  but  can  be  found  in  any  work  on  general 
chemistry. 

The  apparatus  used  in  the  following  tests  may  be  obtained  from 
any  scientific  or  chemist's  supply  house.  For  measuring  out 
samples  a  measuring  glass  or  graduate  is  generally  used  (Fig.  53). 
Greater  accuracy  can  be  obtained  by  using  a  measuring  bottle 
(Fig.  54).  This  is  a  long-necked  bottle  of  a  size  to  hold  a  definite 
quantity  of  liquid  (50  cc.,  100  cc.,  etc.),  when  filled  to  a  mark  in  the 
glass  of  the  neck.  In  use,  the  bottle  is  filled  slightly  above  the 
mark  and  the  surplus  is  removed  by  smartly  jerking  the  bottle. 
Where  the  test  involves  colorimetric  determinations  a  Nessler  tube 
(Fig.  55)  is  used,  the  sample  being  made  up  to  the  mark.  For 
measuring  out  small  quantities  of  liquid  (for  instance,  the  eryth- 
rosin  in  the  alkalinity  test)  pipettes  (Fig.  56)  are  used.  These 
are  made  to  hold  1  cc.,  5  cc.,  10  cc.,  etc.,  up  to  100  cc.  or  more.  The 
pointed  end  is  inserted  into  the  solution  and  the  mouth  is  applied 
to  the  other  end,  the  solution  being  sucked  into  the  pipette  to  a 
little  above  the  mark  on  the  stem.  The  mouth  is  then  removed 
and  a  finger  quickly  substituted  over  the  upper  end.  By  slightly 
releasing  the  pressure  of  the  finger  the  solution  is  allowed  to  run 
out  until  it  stands  just  at  the  mark,  after  which  the  finger  is 
tightly  pressed  over  the  end  and  the  measured  quantity  of  solution 


PHYSICAL    AND    CHEMICAL   TESTS 


99 


is  removed  and  discharged  into  the  sample.  Needless  to  say  it  is 
inadvisable  to  use  a  pipette  in  drawing  off  strong  acids  or  poisons, 
owing  to  the  danger  of  getting  some  in  the  mouth. 

Standard  solutions  are  measured  out  from  burettes  (Fig.  57). 
These  consist  of  glass  tubes  graduated  (generally  to  1/10  cc.),  so 


<3^7 > 


Fig.  53 


Fig.  54 


Fig.  58 


\l 
Fig.  56 


Fig.  57 


Fig.  55 


Folded 


Fig.  59 


that  the  amount  of  solution  run  into  the  sample  can  be  read  off. 
The  initial  reading  (to  1/10  cc.)  is  taken  before  the  test  and  after 
sufficient  solution  has  been  run  into  the  sample  to  produce  the  re- 
quired change  in  color  of  the  indicator  the  burette  is  again  read, 


100  WATER    PURIFICATION    PLANTS 

the  difference  between  the  two  readings  giving  the  number  of 
cc.  of  solution  used.  The  glass  pet  cock  at  the  lower  end  allows 
the  stream  from  the  burette  to  be  regulated.  The  small  glass  bell 
cap  on  top  prevents  evaporation. 

The  sample  during  the  test  may  be  contained  in  a  glass  bottle, 
a  porcelain  casserole  (Fig.  58),  or  dish  (any  white  porcelain  dish  or 
cup  may  be  used),  or  in  a  glass  beaker.  The  latter  is  simply  a 
container  of  thin  glass  (see  Figs.  73  and  75  of  coagulation,  which 
show  typical  beakers).  Generally  a  clear  drinking  glass  or  bottle 
may  be  substituted  for  a  beaker,  unless  it  is  required  to  heat  the 
solution  contained. 

For  special  tests  of  water,  other  than  those  given  here,  the 
reader  is  referred  to  "  Standard  Methods  of  Water  Analysis," 
published  by  the  American  Public  Health  Association,  or  to  any 
standard  work  on  volumetric  analysis. 

Taste  and  Odor.  Many  waters  contain  mineral  constituents 
or  organic  matter  giving  off  tastes  and  odors.  The  odor  of  the 
raw  water  should  be  determined  cold,  that  of  the  filtrate  both  hot 
and  cold.  It  is  not  necessary  to  taste  the  water,  as  the  senses  of 
taste  and  smell  are  very  closely  allied. 

The  cold  odor  is  determined  by  half  filling  a  large  bottle  with 
the  water  and  inserting  the  stopper.  Then  shake  the  bottle 
vigorously,  remove  the  stopper,  and  smell  the  odor  at  the  mouth 
of  the  bottle. 

The  hot  odor  is  determined  by  heating  about  200  cc.  of  the 
sample,  in  a  beaker  covered  with  a  watch  glass,  to  almost  boiling. 
Allow  the  beaker  and  contents  to  cool  for  several  minutes,  remove 
the  watch  glass,  and  smell  the  odor. 

The  odor  may  be  described  in  the  report  by  the  following- 
abbreviations  :* 

v — vegetable  m — moldy 

a — aromatic  M — musty 
g — grassy  d — disagreeable 

f — fishy  p — peaty 

e — earthy  s — sweetish 

Turbidity.  The  generally  accepted  standard  for  turbidity  is 
that  as  measured  by  the  turbidity  rod  of  the  United  States  Geo- 
logical Survey.  This,  as  generally  constructed  (Fig.  59) ,  is  a  hard- 

*"  Standard  Methods    of    Water  Analysis."      American  Public  Health 
Association. 


PHYSICAL   AND    CHEMICAL   TSgTcT 


wood  rod,  half  inch  by  half  inch  in  section,  about  four  feet  long, 
having  a  platinum  wire  of  1  millimeter  (0.04  inch)  diameter  in- 
serted at  right  angles  to  its  length  near  one  end,  and  an  open  sight 
(such  as  a  screw  eye)  at  the  other  end,  1.2  meters  (47 %  inches) 
from  the  wire.  The  wire  should  project  beyond  the  rod  at  least 
one  inch.  The  user  places  his  eye  at  the  sight  and  submerges  the 
wire  end  of  the  rod  into  the  water  to  be  tested  at  right  angles  to  the 
surface.  The  rod  is  pushed  into  the  water  until  the  wire  just  dis- 
appears, as  seen  by  the  observer.  The  turbidity  is  measured  by 
the  submergence  of  the  rod.  A  turbidity  which  causes  the  wire 
to  disappear  with  a  submergence  of  100  millimeters  is  called  100, 
other  turbidities  are  marked  on  the  rod  as  per  the  following  table : 

GRADUATION  OF  TURBIDITY  ROD* 


Turbidity 

Depth  of 
Wire, 
mm. 

Hazen 
Reciprocal 
Scale 

Turbidity 

Depth  of 
Wire, 
mm. 

Hazen 
Reciprocal 
Scale 

10 

794 

0.032 

160 

69 

.37 

15 

551 

.046 

180 

62 

.41 

20 

426 

.060 

200 

57 

.44 

25 

350 

.073 

250 

49 

.52 

30 

296 

.086 

300 

43 

.59 

40 

228 

.111 

350 

39 

.65 

50 

187 

.136 

400 

35 

.72 

60 

158 

.160 

500 

31 

.82 

70 

138 

.184 

600 

28 

.92 

80 

122 

.208 

800 

23 

1.09 

90 

110 

.230 

1,000 

21 

1.21 

100 

100 

.254 

1,500 

17 

1.4$ 

120 

86 

.295 

2,000 

15 

1.72 

140 

76 

.334 

3,000 

12 

2.10 

*  From  the  papers  of  the  U.  S.  Geological  Survey 

In  this  table  the  corresponding  values  for  the  Hazen  Reciprocal 
Turbidity  Rod  have  been  given,  as  this  standard  was  used  in 
making  some  of  the  older  records  and  may  be  convenient  in  re- 
ferring back  to  these. 

Turbidity  measurements  should  be  made  in  the  open,  pref- 
erably during  the  middle  of  the  day  and  not  in  direct  sunlight. 
For  high  turbidities  a  glass  jar  about  6  inches  in  diameter  and 
8  to  10  inches  deep  can  be  used.  For  low  turbidities  a  tank  3  feet 
in  diameter  and  4  feet  deep  or  a  barrel  is  required.  Very  high 
turbidities  must  be  diluted  in  order  to  obtain  accurate  results,  that 
is,  the  sample  is  mixed  with  one  or  more  times  its  volume  of  clear 


WATER    PURIFICATION    PLANTS 

water,  and  the  turbidity  obtained  multiplied  by  a  corresponding 
factor. 

For  convenience  In  laboratory  use,  "  bottle  standards  "  are 
often  prepared*  (Fig.  60).  Take  diatomaceous  earth,  wash  with 
water  to  remove  soluble  salts,  and  ignite  to  remove  organic  matter; 
treat  and  warm  with  dilute  hydrochloric  acid;  wash  with  dis- 


FIG.  60.— Turbidity  Standards. 

tilled  water  to  remove  acid,  and  dry.  Grind  and  sift  through  a 
200-mesh  sieve.  Fill  a  number  of  clear  glass  half-gallon  bottles 
with  distilled  water,  and  add  the  prepared  diatomaceous  earth, 
testing  with  the  turbidity  rod  until  the  desired  turbidity  is  ob- 
tained. Or  one  gram  of  this  powder  can  be  mixed  with  1000 
grams  of  distilled  water  to  give  a  stock  suspension  having  a 
turbidity  of  1000,  and  the  bottle  standards  prepared  from  this  by 
dilution.  Low  turbidities  can  be  obtained  by  dilution  with  dis- 
tilled water.  Standards  having  turbidities  of  3,  5,  10,  15,  20,  30, 
40,  50,  60,  70,  80,  90,  and  100  are  generally  prepared  in  this  way. 
The  bottles  should  be  kept  tightly  corked  and  sealed.  The  water 
to  be  tested  is  put  in  a  bottle  similar  to  those  used  for  the  standards 
and  compared  with  these,  both  sample  and  standard  being  well 
shaken  before  comparison. 

* "  Standard   Methods  of  Water  Analysis."     American    Public    Health 
Association. 


PHYSICAL   AND    CHEMICAL   TESTS  103 

Color.  The  standard  solution  for  color  determination  is  pre- 
pared as  follows:  "  Dissolve  1.246  grams  of  potassium  pla- 
tinic  chlorid  (PtCLi2KCl),  containing  0.5  gram  platinum,  and  one 
gram  crystallized  cobalt  chlorid  (COC126H2O),  containing  0.25 
gram  of  cobalt,  in  water,  with  100  cc.  concentrated  hydrochloric 
acid,  and  make  up  to  one  liter  with  distilled  water."*  This 


FIG.  61. — Color  Standards  and  Rack. 

standard  solution  has  a  color  of  500  parts  per  million.  Slight 
variations  may  be  made  in  the  amount  of  cobalt  chlorid  to  more 
nearly  match  the  color  of  any  particular  water.  From  the  stand- 
ard solution,  dilutions  are  made  with  distilled  water  having  colors 
of  0,  5,  10,  15,  20,  etc.,  up  to  70,  and  these  are  put  into  100  cc, 
Nessler  tubes  of  such  dimensions  that  the  100  cc.  mark  comes 
about  25  cm.  above  the  bottom  and  is  uniform  in  all  the  tubes. 
The  solution  must  be  up  to  the  100  cc.  mark  and  the  tubes  should 
be  corke'd  when  not  in  use  to  prevent  evaporation  and  the  entrance 
of  dust.  The  tubes  are  placed  in  a  vertical  position  in  a  "  color 
rack  "  (which  can  be  obtained  from  any  dealer  in  chemical  ap- 
paratus), resting  on  a  white  porcelain  plate  or  slab. 

The  water  to  be  tested  is  first  filtered  to  remove  the  turbidity 

"  Standard  Methods  of   Water  Analysis."      American  Public  Health 
Association. 


104  WATER   PURIFICATION    PLANTS 

and  then  poured  into  a  100  cc.  Nessler  tube  similar  to  those  in  the 
rack.  For  comparison  it  is  placed  next  to  those  in  the  rack,  the 
color  being  determined  by  looking  downward  into  the  upper  ends 
of  the  tubes  against  the  white  porcelain  slab  beneath.  It  is  thus 
compared  successively  with  the  various  standard  tubes,  the  results 


FIG.  62. — Apparatus  for  Alkalinity  Test. 

being  recorded  as  that  of  the  standard  to  which  the  color  of  the 
sample  most  nearly  agrees. 

Alkalinity.  Apparatus :.  1-100  cc.  burette,  graduated  to  1/10  cc. 
for  £-0  sulphuric  acid  (H2S04);  1-100  cc.  burette,  graduated  to 
1/10  cc.  for  ^  sodium  carbonate  (Na2CO3);  1-250  cc.  clear  glass, 
wide-mouthed,  glass-stoppered  bottle;  1-100  cc.  measuring  glass 
or  flask. 


PHYSICAL   AND    CHEMICAL   TESTS  105 

Reagents:  ^  sulphuric  acid;  ^  sodium  carbonate;  erythrosin 
solution  (0.1  gram  of  the  sodium  salt  in  one  liter  distilled  water); 
chloroform,  neutral  to  erythrosin. 

Procedure:  With  a  graduated  glass  or  flask  measure  100  cc. 
of  the  sample  to  be  tested  into  the  250  cc.  glass-stoppered  bottle, 


FIG.  63. — Apparatus  for  Free  Carbonic-Acid  Test. 

add  1  cc.  of  erythrosin  with  a  pipette  and  5  cc.  of  chloroform. 
Cork  the  bottle  and  shake  well.  If  the  sample  has  a  pink  color  it 
is  alkaline.  In  that  case  titrate  with  ^  sulphuric  acid,  adding  a 
little  at  a  time,  and  shaking  well  after  each  addition.  Continue 
to  add  the  acid  until  the  pink  color  disappears.  The  number  of 
cubic  centimeters  of  sulphuric  acid  added,  multiplied  by  10,  gives 
the  alkalinity  in  parts  per  million. 


106  WATER    PURIFICATION    PLANTS 

In  case  the  sample  remains  white  after  adding  the  erythrosin, 
it  is  acid,  and  should  be  titrated  in  a  similar  manner,  using  the  ^ 
sodium  carbonate.  The  number  of  cubic  centimeters  of  sodium 
carbonate  used,  multiplied  by  10,  gives  the  acidit'T  in  parts  per 
million  as  H2SO^. 

Remarks:  For  strict  accuracy,  a  correction  should  be  applied 
for  the  alkalinity  of  the  erythrosin.  This  correction  can  be 
obtained  by  running  a  test  as  above  with  distilled  water,  when 
the  alkalinity  obtained  will  be  that  due  to  the  erythrosin.  In  gen- 
eral, this  correction  is  about  1  part  per  million,  to  be  subtracted 
for  alkaline  samples  and  added  for  acid  samples. 

The  chloroform  used  can  be  recovered  by  emptying  the  samples 
into  a  wide-mouthed  bottle  after  the  test.  The  chloroform  col- 
lects in  the  bottom  of  the  bottle,  the  water  above  can  be  decanted 
from  time  to  time,  and  when  sufficient  chloroform  has  collected  it 
can  be  recovered  by  redistillation. 

If  the  sample  is  very  turbid,  it  should  be  filtered  before  the  test, 
so  that  the  action  of  the  indicator  will  not  be  obscured. 

Free  Carbonic  Acid.  Apparatus:  1-100  cc.  burette,  graduated 
to  1/10  cc.  for  ^  sodium  carbonate*  1-250  cc.  porcelain  dish  or 
casserole;  glass  stirring  rod. 

Reagents:  ^  sodium  carbonate  (Na2C03)  and  phenolphthalein 
solution  (1  gram  in  200  cc.  of  50-per-cent  alcohol). 

Procedure:  Pour  100  cc.  of  the  sample  into  the  procelain  dish 
and  add  a  few  drops  of  phenolphthalein.  If  the  water  remains 
colorless  it  contains  carbonic  acid.  In  that  case,  add  sodium  car- 
bonate from  the  burette  slowly,  gently  stirring  the  water  mean- 
while. Continue  adding  sodium  carbonate  until  a  faint,  per- 
manent pink  color  appears  in  the  water.  The  number  of  cubic 
centimeters  of  sodium  carbonate  added,  multiplied  by  4.4,  gives 
the  amount  of  free  carbonic  acid  (as  CO2)  in  parts  per  million. 

Remarks:  To  obtain  accurate  results,  it  is  very  important 
that  in  collecting  the  sample,  carrying  it  to  the  laboratory,  and  in 
conducting  the  test,  it  be  as  little  agitated  as  possible,  since  the 
free  CO2  readily  escapes.  The  stirring  rod  should  be  used  gently, 
merely  to  mix  the  reagent  through  the  sample.  A  rubber-tipped 
stirring  rod  can  be  used  to  advantage. 

As  in  the  alkalinity  test,  a  very  turbid  water  can  be  filtered 
before  the  test,  but  this  must  be  accomplished  with  the  least 
possible  agitation, 


PHYSICAL   AND    CHEMICAL   TESTS  107 

In  acid  waters  erroneous  results  will  be  obtained,  due  to  the 
phenolphthalein  indicating  the  acids  as  well  as  the  CO2.  In  such 
a  case,  run  the  test  as  above  outlined,  then  subtract  from  the 
reading  in  cubic  centimeters  of  sodium  carbonate  required  to 
obtain  a  pink  coloration  with  phenolphthalein,  two  times  the 
number  of  cubic  centimeters  required  for  the  acid  test  with 
erythrosin,  and  multiply  the  remainder  by  4.4  to  obtain  the 
parts  per  million  of  CO2. 

Example:  Acidity  test  with  erythrosin  required  10  cc.  of  ^ 
Na2CO3 

CO2  test  with  phenolphthalein  required     25  cc. 
2  X   10  cc.  =  20  cc. 


Subtracting  5  cc. 

Multiplying  by  4.4 


Parts  per  million  C02  22.0 

The  same  result  can  be  obtained  by  determining  the  amount 
of  sodium  carbonate  required  with  phenolphthalein,  then  taking 
a  second  sample,  boiling  off  the  free  carbonic  acid,  and  repeating 
the  test.  The  difference  between  the  two  tests,  in  cubic  centi- 
meters, multiplied  by  4.4,  will  give  the  CO2  in  parts  per  million. 

Swamp  waters  and  others  containing  weak  organic  acids  may 
give  slightly  erroneous  results  in  the  above  test,  but  this  error  is 
generally  relatively  unimportant. 

By  means  of  Plate  I,  the  results  of  alkalinity,  acidity,  and  CO2 
tests  can  be  determined  graphically  from  the  burette  readings. 
In  this  chart  the  necessary  corrections  for  the  effect  of  reagents 
and  the  presence  of  acids  in  the  free  carbonic-acid  test  are  made. 
The  chart  is  ruled  with  a  series  of  horizontal  lines  corresponding  to 
the  number  of  cubic  centimeters  of  reagent  required  in  making  the 
test.  There  is  also  a  series  of  vertical  lines  corresponding  to  the 
results  required  in  parts  per  million,  as  indicated  by  the  figures 
along  the  lower  margin.  Three  heavy  diagonal  lines  are  drawn 
across  the  chart,  representing  respectively  the  relation  of  the  de- 
sired result  in  parts  per  million  to  the  cubic  centimeters  of  reagent 
used,  for  the  free  carbonic-acid  test,  titrating  with  one-fiftieth 
normal  sodium  carbonate  and  phenolphthalein  indicator,  for  the 
alkalinity  test  and  for  the  acidity  test,  with  (in  both  cases)  eryth- 


108  WATER   PURIFICATION    PLANTS 

rosin  as  indicator,  and  one-fiftieth  normal  sulphuric  acid  and  sodi- 
um carbonate  respectively.  The  fine  diagonal  lines  in  the  lower  left 
corner  are  for  use  in  correcting  the  carbonic-acid  results  in  acid 
water.  The  uses  of  this  chart  are  best  illustrated  by  examples : 

Example  No.  1.  Alkalinity  Test  with  Erythrosin.  In  test- 
ing a  water  for  alkalinity  according  to  instructions  given  on  page 
104,  12.60  cubic  centimeters  of  ^  sulphuric  acid  are  required  to 
discharge  the  pink  color  of  the  erythrosin.  Look  along  the  left- 
hand  margin  of  the  chart  for  the  horizontal  line  corresponding  to 
12.6.  As  each  horizontal  line  represents  two-tenths  of  a  cubic 
centimeter  of  reagent,  the  required  line  is  the  third  above  the 
heavy  line  marked  12.  Follow  this  horizontal  line  toward  the 
right  until  it  crosses  the  diagonal  line  marked  "  Alkalinity  with 
1  cc.  Erythrosin."  This  intersection  occurs  midway  between 
two  vertical  lines.  Following  downward  between  these  lines  to 
the  lower  margin,  this  is  intersected  two  and  one-half  spaces  be- 
yond the  120  line.  As  each  space  on  the  lower  margin  corresponds 
to  two  parts  per  million,  the  result  of  the  test,  in  parts  per  million, 
is  125. 

Example  No.  2.  Acidity  Test  with  Erythrosin.  In  a  test 
made  according  to  instructions  on  page  104,  6  cubic  centimeters 
were  required  before  the  pink  color  of  the  erythrosin  appeared. 
Look  along  the  left-hand  margin  of  the  chart,  below  the  zero  line, 
and  find  6  on  the  scale  marked  "  f-Q  Sodium  Carbonate  in  CC." 
Follow  this  line  horizontally  toward  the  right  until  the  diagonal 
line  marked  "  H2S04  Acidity  with  1  cc.  Erythrosin  "  is  intersected. 
This  occurs  midway  between  two  vertical  lines.  Following  down- 
ward between  these  to  the  lower  margin,  this  is  intersected  one-half 
space  beyond  the  heavy  vertical  line  marked  60.  As  each  space 
on  the  lower  margin  corresponds  to  two  parts  per  million,  the 
result  of  the  test,  in  parts  per  million,  is  61. 

Example  No.  3.  Test  for  Free  CO2  with  Phenolphthalein.  In 
making  a  test  for  free  C02  in  accordance  with  instructions  on  page 
106,  7  cubic  centimeters  of  reagent  were  used  to  produce  a  pink 
color.  In  the  left-hand  margin  of  the  chart  find  7  in  the  column 
marked  "  Reagent  Required  in  Cubic  Centimeters."  Tracing  to 
the  right  along  the  horizontal  line  through  this  point,  until  the 
diagonal  marked  "  Free  CO2  with  Phenolphthalein  "  is  reached, 
follow  downward  along  the  vertical  line  through  this  intersection, 
and  at  the  lower  margin  find  30.8  as  the  result  in  parts  per  million. 


PHYSICAL   AND    CHEMICAL   TESTS  109 

Example  No.  4.    Test  for  Free  CO2  in  an  Acid  Water.     As- 

suming that  it  is  desired  to  test  for  free  CO2  a  sample  of  water 
which  has  an  acidity  with  erythrosin  of  24  parts  per  million 
(requiring  2.4  cubic  centimeters  of  ^  Na^COs  to  neutralize).  It 
is  found  to  require  7.1  cubic  centimeters  of  g^  Na^COs  to  produce 
a  pink  color  phenolphthalein.  In  the  scale  on  the  left-hand  margin 
estimate  the  point  corresponding  to  7.1  (7  is  the  line  midway  be- 
tween 6  and  8;  7.1  would  be  1/20  of  a  space,  a  very  small  distance, 
above  this).  Follow  this  line  horizontally  toward  the  right  until 
the  "  Free  CO2  "  diagonal  is  reached.  This  occurs  about  midway 
between  two  vertical  lines.  Follow  downward  between  these  until 
the  horizontal  line  under  "  O  "  in  the  left-hand  scale  is  reached. 
From  this  point  continue  downward  and  toward  the  left,  parallel 
to  the  light  diagonals  until  the  horizontal  line  through  2.4  cc.  on  the 
"  ^  Sodium  Carbonate  "  scale  is  reached.  (This  horizontal  is  the 
second  line  below  "  2  "  on  this  scale,  as  each  space  represents 
0.2  cc.  of  reagent.)  From  this  intersection  follow  vertically  down- 
ward to  the  lower  margin,  where  the  result  in  parts  per  million  is 
found  to  be  10. 

Alkalimetry  and  Indicators.  The  tests  for  alkalinity  and  CO2 
involve  the  use  of  alkalimetry  (or  acidimetry)  and  indicators. 
The  bases  (as  sodium  hydroxid  (NaOH)  and  calcium  hydroxid 
(Ca(OH)2)  and  certain  salts  cause  alkaline  reaction  in  water  due  to 
the  presence  of  hydroxyl  (OHO  ions.  The  salts  give  this  reaction 
by  interaction  with  the  water,  a  phenomenon  known  as  hydrolysis. 
As  an  example  of  this  interaction  take  a  solution  of  sodium  car- 
bonate in  water;  the  salt  is  ionized  as  Na"  and  CO3",  the  water 
slightly  as  H*  and  OH'.  The  two  possible  products  are  sodium 
hydroxid  (NaOH)  and  carbonic  acid  (H2C03).  The  latter  is  a 
weak  acid  —  very  slightly  ionized  —  which  does  not  affect  the  prop- 
erties of  the  solution.  The  sodium  hydroxid  is  ionized  to  a  much 
greater  extent,  giving  the  water  an  alkaline  reaction.  This  inter- 
action may  be  represented  schematically  : 


2H2O      <=»2H'    +  2OH'j 

Other  salts,  which  by  hydrolytic  action  with  water  produce  a 
highly  ionized  acid,  give  the  water  an  acid  reaction.  Thus  the 
hydrolysis  of  aluminum  sulphate  is  as  follows  : 


110 


WATER    PURIFICATION    PLANTS 


6H20 


•••+3S04"  1 
•    +  6OH' 


3H2S04 


The  indicators  used,  phenolphthalein  and  erythrosin,  have  the 
faculty  of  indicating  the  presence  of  a  small  excess  of  either 
hydroxyl  ions  (OH')  or  hydrions  (H)  by  changes  of  color.  The 
phenolphthalein  (Ci4HioO4),  a  colorless  substance  and  very  feebly 
acid,  is  not  perceptibly  dissociated  in  solution: 

Ci4H10O4  (colorless)  <F±  Ci4H9O4'  (red)  +  H' 

In  the  presence  of  an  alkaline  salt  the  H  ion  combines  with  the 
OH'  ion  present  and  the  above  equilibrium  is  displaced  forward, 
and  a  visible  amount  of  the  red  negative  ion  is  formed. 

The  action  of  these  two  indicators  with  substances  commonly 
met  with  in  the  above  tests  is  as  follows  : 


Substance 

Color 

with 
Erythrosin 

Color 
with 
Phenolphth  alein 

Sulphuric  acid,  H2SO  

Colorless 

Colorless 

Ferrous  sulphate,  FeSO4  

Colorless 

Colorless 

Aluminum  sulphate  A12(SO4)3 

Colorless 

Colorless 

Carbonic  acid  H2CO3 

Not  indicated 

Colorless 

Sodium  bicarbonate,  NaHCO3 

Pink 

Not  indicated 

Calcium  bicarbonate,  CaH9(CO3),  

Pink 

Not  indicated 

Sodium  carbonate  Na^CO? 

Pink 

Pink 

Calcium  carbonate,  CaCO3  
Sodium  hydroxid,  NaOH  

Pink 
Pink 

Pink 
Pink 

Calcium  hydroxid,  Ca(OH)2  

Pink 

Pink 

Sodium  chlorid   NaCl 

Not  indicated 

Not  indicated 

Sodium  sulphate  Na2SO4 

Not  indicated 

Not  indicated 

Calcium  sulphate,  CaSO4 

Not  indicated 

Not  indicated 

From  this  tabulation  it  is  seen  that  phenolphthalein  is  a  most 
delicate  indicator  with  acids,  indicating  even  carbonic  acid.  Its 
use  in  determining  the  acidity  of  a  water  would  be  confusing,  as 
it  would  be  affected  by  carbonic  and  weak  organic  acids  present. 
Erythrosin  indicates  both  sulphuric  acid  and  the  acid  sulphates 
of  aluminum  and  iron.  If  it  is  desired  to  determine  the  free  sul- 
phuric acid  only,  a  less  delicate  indicator — methyl  orange* — 

*  Methyl-orange  indicator  is  made  by  dissolving  1/10  gram  of  the  com- 
pound (also  known  as  Orange  III)  in  a  few  cubic  centimeters  of  alcohol  and 
diluting  to  100  cc.  with  distilled  water.  The  100  cc.  sample  to  be  tested  for 
acidity  is  titrated  in  the  cold  with  sodium  carbonate  solution  (^)  using  a  few 
drops  of  methyl  orange  as  an  indicator.  The  methyl  orange  gives  a  red  color 
with  acid  water,  which  changes  to  yellow  when  the  acid  is  neutralized. 


PHYSICAL   AND    CHEMICAL   TESTS  111 

must  be  used  instead  of  erythrosin  and  chloroform,  in  the  test  for 
acidity. 

The  table  also  shows  that  alkalinity  may  be  due  to  the  bicar- 
bonates, carbonates,  and  hydroxids  of  the  alkalies  and  alkaline 
earth  metals.  Bicarbonates  in  an  untreated  water  are  generally 
attributed  to  calcium  (Ca)  and  magnesium  (Mg),  while  car- 
bonates are  attributed  to  sodium  (Na)  and  potassium  (K),  as  the 
carbonates  of  these  metals  are  soluble  in  water,  whereas  those  of 
calcium  and  magnesium  are  only  very  sparingly  soluble.  If  there 
is  a  sufficiency  or  surplus  of  carbonic  acid  present,  all  the  alkalinity 
will  exist  as  bicarbonates.  Bicarbonates  and  hydroxids  cannot 
exist  together,  as  they  react  chemically,  forming  carbonates  and 
water.  It  will  be  noted  that  erythrosin  indicates  all  three  kinds 
of  alkalinity,  whereas  phenolphthalein  indicates  only  carbonates 
and  hydroxids.  Another  peculiarity  of  the  alkalinity  with  phenol- 
phthalein arises  from  the  fact  that  it  does  not  indicate  bicarbonates. 
The  reaction  in  neutralizing  alkalinity  with  standard  sulphuric 
acid  may  be  represented  by  the  equations: 

CaCO3  +  H2SO4  =  CaSO4  +  H2CO3 
CaCO3  +  H2CO3  =  CaH2  (CO3)2 

Thus  one  unit  of  sulphuric  acid  neutralizes  two  units  of  carbonates 
as  indicated  by  phenolphthalein.  The  following  rules  for  de- 
termining the  three  types  of  alkalinity  may  be  given: 

1.  When  an  alkaline  water  is  neutral  or  acid  with  phenolphtha- 
lein the  alkalinity  is  due  to  bicarbonates. 

2.  When  the  phenolphthalein  alkalinity  is  less  than  half  of  the 
erythrosin  alkalinity,  twice  the  phenolphthalein  alkalinity  gives 
the  carbonates,  the  difference  between  these  and  the  erythrosin 
alkalinity  gives  the  bicarbonates. 

3.  When  the  phenolphthalein  alkalinity  is  one-half  the  eryth- 
rosin alkalinity,  carbonates  only  are  present. 

4.  When  the  phenolphthalein  alkalinity  is  more  than  half 
the  erythrosin   alkalinity,  hydroxids  are  present.     To  find   the 
amount,  multiply  the  difference  between  the  two  alkalinities  by 
two  and  subtract  this  from  the  erythrosin  alkalinity.     The  re- 
maining alkalinity  is  due  to  carbonates. 

5.  When  the  phenolphthalein  and  erythrosin  alkalinities  are 
equal,  only  hydroxids  are  present. 

Knowing  the  alkalinity  of  a  water  with  phenolphthalein  and 


112  WATER   PURIFICATION    PLANTS 

with  erythrosin,  the  bicarbonates,  carbonates,  and  hydroxids  can 
be  determined  graphically  from  Plate  II.  The  horizontal  lines  re- 
present phenolphthalein  alkalinity,  as  indicated  by  the  scale  on 
the  left-hand  margin,  each  space  being  equivalent  to  one  part  per 
million.  The  diagonal  lines  represent  erythrosin  alkalinity,  each 
space  being  equivalent  to  5  parts  per  million.  The  vertical  lines 
represent  the  components  of  these  alkalinities  as  bicarbonates 
(lower  margin,  toward  the  left),  hydroxids  (lower  margin  toward 
the  right),  and  carbonates  (upper  right  margin).  The  following 
examples  will  illustrate  the  use  of  this  chart: 

Example     No.      1.      Given     a     water     of     the     following 
characteristics : 

Phenolphthalein  alkalinity  -      25 
Erythrosin  alkalinity  -  100 

Find  25  on  the  scale  along  the  left-hand  margin  (the  heavy  line 
midway  between  20  and  30),  and  follow  the  line  through  this  point 
horizontally  to  the  right  until  the  erythrosin  diagonal  marked 
100  is  reached.  By  following  the  vertical  through  this  point 
downward  to  the  lower  margin,  the  bicarbonate  alkalinity  is  found 
to  be  50  (midway  between  40  and  60).  If  the  horizontal  line 
through  25  is  followed  further  to  the  right,  it  will  be  found  to  take 
a  sharp  upward  turn,  and  continuing  along  this  to  the  upper  mar- 
gin the  carbonate  alkalinity  of  the  water  is  found  to  be  50 
also. 

Example     No.     2.      Given     a     water     of     the     following 
characteristics : 

Phenolphthalein  alkalinity  —  40 
Erythrosin  alkalinity  -  60 

Find  40  on  the  scale  along  the  left-hand  margin,  and  follow  this 
line  horizontally  to  the  right  until  it  intersects  the  erythrosin 
diagonal  marked  60.  Following  the  vertical  line  through  this 
point  downward  to  the  lower  margin,  the  water  is  found  to  have  a 
hydroxid  or  caustic  alkalinity  of  20  parts  per  million.  Following 
the  heavy  diagonal  line  through  this  same  point  of  intersection 
upward  to  the  upper  margin,  the  carbonate  alkalinity  is  found  to 
be  40  parts  per  million. 

The  above  determinations  are  in  terms  of  calcium  carbonate. 


PHYSICAL   AND    CHEMICAL   TESTS  113 

More    properly    they    should  be  multiplied     by    the    following 
factors : 


Substance  as 
CaC03 

Multiply  By 

Gives  Result  As 

Bicarbonates  .  .  . 
Carbonates  .... 
Hydroxids 

1.62 
1.06 
0  74 

Calcium  bicarbonate  (CaH2(CO3)2) 
Sodium  carbonate  (Na2CO3) 
Calcium  hydroxid  (Ca(OH)>) 

Sometimes  it  is  desirable  to  determine  the  "  half-bound  "  and 
"bound  "  carbonic  acid  (CO2).  To  obtain  these  data,  multiply  the 
bicarbonates  and  carbonates  respectively  (in  terms  of  calcium 
carbonate)  by  0.44.  It  is  not  correct  to  record  bicarbonates  and 
half -bound  CO2,  or  carbonates  and  bound  C02,  in  an  analysis,  as  the 
one  includes  the  other  in  both  cases.  Free  C02,  however,  is  an 
independent  substance,  as  its  name  implies. 

Iron.  Apparatus:  1-100  cc.  measuring  glass;  1-250  cc.  porcelain 
evaporating  dish;  100  cc.  Nessler  tubes,  IJ/g  mcn  diameter  by  5J4 
inches  high  to  100  cc.  mark  (at  least  twelve  are  required  for  per- 
manent standards);  1-100  cc.  burette,  graduated  to  1/10  cc.  for 
standard  iron  solution. 

Reagents:  Hydrochloric  acid  (1:1);  nitric  acid  (1:2);  potas- 
sium permanganate  solution  (5  gm.  per  liter);  potassium  sulpho- 
cyanid  solution  (20  gm.  per  liter);  standard  iron  solution  ("dissolve 
0.7  gram  of  crystallized  ferrous  ammonium  sulphate  in  50  cc.  of 
distilled  water  and  add  20  cc.  of  dilute  sulphuric  acid.  Warm 
the  solution  slightly  and  add  potassium  permanganate  until  the 
iron  is  completely  oxidized.  Dilute  the  solution  to  one  liter."* 
One  cc.  of  this  standard  solution  in  100  cc.  of  distilled  water  is 
equal  to  one  part  per  million  of  iron). 

Procedure:  Boil  100  cc.  of  the  sample  several  minutes  in  an 
evaporating  dish  with  5  cc.  nitric  acid.  Add  two  or  three  drops 
of  the  potassium  permanganate  solution  and  allow  to  stand  a  few 
minutes.  If  the  red  color  disappears,  add  more  permanganate,  drop 
by  drop,  until  a  faint  pink  color  persists.  Add  10  cc.  of  the  potas- 
sium sulphocyanid  solution,  mix  thoroughly,  and  pour  into  a  100  cc. 
Xessler  tube.  Pour  100  cc.  of  distilled  water  into  a  second 
Nessler  tube,  add  5  cc.  of  nitric  acid  and  10  cc.  of  potassium 

"  Standard  Methods  of  Water  Analysis."      American  Public  Health 
Association. 


114  WATER    PURIFICATION    PLANTS 

sulphocyanid.  Add  standard  iron  solution  to  the  second  Nessler 
tube  until  the  color  of  its  contents  matches  that  of  the  sample. 
The  number  of  cc.  of  iron  standard  added  gives  the  dissolved  iron 
in  parts  per  million. 

If  the  sample  contains  organic  matter,  it  must  be  treated  as 
follows:  after  filtering,  evaporate  to  dryness  and  ignite  to  destroy 


FIG.  64. — Apparatus  for  Iron  Test. 

organic  matter;  cool  and  add  5  cc.  of  hydrochloric  acid  (1:1)  to 
residue,  and  if  this  is  not  dissolved  immediately,  heat  gently;  wash 
the  liquid  into  a  100  cc.  Nessler  tube,  and  make  up  to  100  cc. 
with  distilled  water:  then  add  potassium  permanganate  and  sul- 
phocyanid and  proceed  as  before,  using  hydrochloric  acid  in  the 
second  Nessler  tube  also. 


PHYSICAL    AND    CHEMICAL   TESTS 


115 


If  desired,  permanent  iron  standards,  similar  to  the  color 
standards  herein  before  described,  can  be  made  up.  The  follow- 
ing solutions  are  required.* 

Platinum  solution:  12  grams  of  potassium  platinic  chlorid 
(PtCl4,2KCl),  dissolved  in  distilled  water,  with  the  addition  of 
100  cc.  strong  hydrochloric  acid,  and  made  up  to  one  liter  with 
distilled  water. 

Cobalt  solution:  24  grams  of  cobaltous  chlorid  crystals 
(CoCl2,6H20),  dissolved  in  distilled  water,  with  the  addition  of 
100  cc.  strong  hydrochloric  acid,  and  made  up  to  one  liter  with 
distilled  water.  The  standards  are  made  up  by  the  addition  of 
various  amounts  of  these  solutions  to  distilled  water  in  the  100  cc. 
Nessler  tubes  described  under  "  Apparatus,"  as  follows: 


Standard 

Standard 

Iron 

No.  of  CC. 

No.  of  CC. 

Iron 

No.  of  CC. 

No.  of  CC. 

Solution, 

Platinum 

Cobalt 

Solution, 

Platinum 

Cobalt 

Parts  per 

Solution 

Solution 

Parts  per 

Solution 

Solution 

Million 

Million 

0.0 

0 

.0 

1.5 

28 

17.0 

0.1 

2 

1.0 

2.0 

35 

24.0 

0.3 

6 

3.0 

2.5 

39 

32.0 

0.5 

10 

5.0 

3.0 

40 

43.0 

0.7 

14 

7.5 

3.5 

40 

55.0 

1.0 

20 

11.0 

4.0 

40 

67.0 

In  each  case  the  platinum  and  cobalt  solutions  are  poured  into  the 
Nessler  tube  first  and  enough  distilled  water  is  added  to  make  up 
the  solution  to  the  100  cc.  mark.  The  water  to  be  tested  is  treated 
as  before,  and  after  adding  the  potassium  sulphocyanid  is  im- 
mediately compared  with  the  permanent  standards. 

Logwood  Test  for  Free  Alum  and  Iron.  Apparatus:  Two 
250  cc.  porcelain  dishes  or  casseroles. 

Reagents:  Solution  of  logwood  in  distilled  water;  acetic  acid 
(glacial) . 

Procedure:  Pour  100  cc.  of  water  to  be  tested  into  each  of 
two  porcelain  dishes.  To  the  second  dish  add  a  small  piece  of 
alum  or  iron  sulphate,  and  run  this  dish  as  a  control,  to  check  the 
color  changes  in  the  sample  being  tested.  Add  a  few  drops  of  log- 
wood solution  to  each  dish,  stir  gently,  and  observe  the  colors. 
Then  add  a  few  drops  of  acetic  acid  to  each  dish,  stir,  and  note  the 


*  Jackson,  Tech.  Quar.,  13,  p.  320. 


116  WATER   PURIFICATION   PLANTS 

color  changes.  The  colors  obtained  vary  slightly  with  different 
waters,  thence  the  need  for  running  the  check  sample  containing 
alum  or  iron  along  with  the  water  being  tested.  Approximately 
the  following  color  changes  occur:  If  alum  is  present:  when  log- 
wood is  added,  the  water  turns  blue,  when  acetic  acid  is  added  the 
blue  changes  to  red,  fading  gradually  to  yellow.  If  no  alum  is 
present:  when  logwood  is  added,  the  water  turns  red,  when  acetic 
acid  is  added,  it  changes  to  yellow.  If  iron  is  present :  when  log- 
wood is  added,  the  water  turns  a  greenish  black,  when  acetic  acid 
is  added  the  same  color  persists,  changing  gradually  to  yellow.  If 
no  iron  is  present,  the  color  changes  are  the  same  as  when  no  alum 
is  present. 

Test  for  Excess  of  Hypochlorite  of  Lime.  Where  a  water  is 
being  sterilized  with  hypochlorite  of  lime,  the  following  test  may  be 
used  to  indicate  an  excess  in  the  treated  water.*  Fill  a  quart 
bottle  with  the  treated  water,  add  a  small  crystal  of  potassium 
iodid  (K  I),  a  few  drops  of  weak  acetic  acid,  and  a  teaspoonful  of 
starch  solution  and  shake  thoroughly.  A  blue  tint  indicates  an 
excess  of  hypochlorite,  a  violet  tint  shows  that  the  amount  being 
used  is  not  excessive.  The  starch  solution  is  made  by  boiling  one 
part  of  starch  in  200  of  water  for  several  minutes.  Add  a  few  drops 
of  chloroform  to  preserve  the  solution.  The  bacterial  test  for 
sterility  is  most  important,  the  above  test  being  merely  confirma- 
tory and  for  use  where  facilities  for  bacterial  work  are  absent. 

Test  for  Strength  of  Hypochlorite  Solutions.  Place  10  cc.  of 
the  solution  to  be  tested  in  a  beaker  or  glass  and  slowly  run  in 
1/10  alkaline  arsenite  solution, f  stirring  contents  with  a  glass  rod. 
At  frequent  intervals,  a  drop  of  the  solution  is  removed  on  the 
glass  rod  and  brought  into  contact  with  prepared  starch  paper.  | 
Continue  titration  until  no  blue  color  is  produced  on  the  paper  in 
this  way.  The  cubic  centimeters  of  arsenite  solution  used  multi- 
plied by  0.0355  gives  the  available  chlorine  in  per  cent. 

*  G.  S.  Woodhead,  Surveyor,  July  22,  1910. 
f  See  Appendix  B  for  preparation. 


CHAPTER  IV 

BACTERIAL  TESTS 

THE  making  of  bacterial  tests  requires  considerable  time,  and 
for  this  reason  it  is  often  customary  in  small  plants  to  send  weekly 
or  biweekly  samples  to  some  reliable  testing  laboratory  for  bac- 
terial counts  and  coli  determinations.  This  cannot  be  recom- 
mended as  the  best  plan,  since  it  does  not  afford  a  continuous 
record  of  the  bacterial  efficiency  of  the  filters,  and,  between  sam- 


FIG.  65a—  Dry  Sterilizer  (closed). 

plings,  the  output  may  be  high  in  bacteria  for  several  days  without 
the  knowledge  of  the  operator.  Generally,  bacterial  determina- 
tions should  be  made  daily.  It  is  now  possible  to  secure  the 
necessary  media,  tubed  ready  for  use,  at  most  of  the  scientific 
supply  houses,  which  would  effect  a  saving  of  time  in  the  case  of 
the  smaller  plants,  where  the  operator  must  look  after  the  testing, 

117 


118 


WATER    PURIFICATION    PLANTS 


although  this  is  more  expensive  than  preparing  the  media  in  the 

laboratory. 

Apparatus.     The  following  is  the  essential  apparatus  required: 
1.  Dry  Sterilizer,  for  sterlizing  glassware.     This  consists  of  a 


FIG.  656. — Dry  Sterilizer  (open). 


FIG.  66. — Steam  Sterilizers. 


sheet-metal  oven,  provided  with  shelves  for  the  apparatus,  and 
heated  by  a  gas  flame  underneath.  A  thermometer  is  provided 
for  noting  the  temperature  of  sterilization.  In  use,  the  bottom 


BACTERIAL    TESTS 


119 


shelf  should  be  covered  with  asbestos,  to  prevent  overheating 
the  glassware,  and  care  should  be  taken  that  the  gas  flame  is 
non-luminous,  otherwise  the  apparatus  will  be  covered  with 
soot. 

2.  Steam  Sterilizer,  or  "  arnold  "  (from  the  inventor's  name) 
for  sterilizing  media.  It  consists  of  a  water-pan  surmounted  by  a 
metal  cylinder  containing  trays  for  holding  flasks  and  tubes  of 

media.  In  operation  a  gas 
flame  below  the  water-pan 
generates  steam,  which  flows 
upward  among  the  bottles  of 
media  and  is  condensed  against 
the  cover  of  the  cylinder,  the 
condensate  flowing  back  into 
the  pan.  Media  are  sterilized 
by  subjecting  them  to  the  steam 
in  this  manner  for  thirty  min- 
utes on  three  successive  days. 
It  is  necessary  to  use  this 
method  of  sterilization  for  all 
media  containing  sugar,  to  pre- 
vent its  "  inversion."  It  can 
be  used  for  all  media,  but  the 
autoclave  saves  considerable 
time. 

3.  The  Autoclave  is  used 
to  sterilize  media  under  steam 
pressure,  a  more  convenient 
way  than  the  one  above  de- 
scribed. It  consists  of  a  strong 
cylinder,  provided  with  an  air- 
tight cover.  The  lower  part 
of  the  cylinder  is  filled  with 
water,  above  which  the  flasks 
and  tubes  of  media  rest  on  trays.  The  water  is  heated  by  a 
gas  flame  under  the  cylinder.  A  valve  is  provided  in  the  cover 
through  which  to  allow  the  air  to  escape  when  the  autoclave  is 
started,  also  a  thermometer  to  give  the  temperature  of  the  steam. 
After  a  batch  of  media  has  been  sterilized,  the  pressure  must  be 
allowed  to  die  down  before  opening  the  autoclave,  otherwise  the 


FIG.  67. — Autoclave. 


120 


WATER    PURIFICATION    PLANTS 


plugs  will  be  blown  from  the  flasks  and  tubes  by  the  steam  pressure 
within  them. 

4.  A  Small  Ice  Box  of  the  ordinary  type  is  useful  for  storing 
media. 

5.  Incubators.     These   consist  of    water- jacketed  boxes,   ar- 
ranged with  shelves  and  provided  with  double  doors,  the   inner 


FIG.  68a. — 37°  C.  Incubator  (closed). 

one  of  glass,  so  that  the  cultures  may  be  observed  without  admit- 
ting cold  air.  The  contents  are  kept  at  a  uniform  temperature  by 
an  automatically  regulated  gas  flame  or  by  electric  light  bulbs. 
The  incubators  should  be  well  ventilated  and  should  contain  a 
pan  of  water  to  keep  the  air  moist.  Two  are  required,  one  for 
20°  C.  and  one  for  37°  C.  incubation.  As  steam-heated  rooms 


BACTERIAL    TESTS 


121 


can  be  kept  at  a  very  uniform  temperature,  as  an  expedient  20° 
cultures  can  be  incubated  in  the  laboratory,  placing  them  in  a 
box  containing  a  pan  of  water.  (20°  C.  =  68°  Fahr.) 

6.  A  two-burner  gas  stove — for  preparing  media. 

7.  Several  asbestos  hot  plates,  for  use  with  the  gas  stove. 


FIG.  686.— 37°  C.  Incubator  (open). 

8.  Several  enameled  rice  boilers  of  3-  to  4-pint  capacity,  for 
preparing  media. 

9.  Balance,  two-pan  type,  0-2000  grams,  for  weighing  media. 

10.  One  Bunsen  microburner. 

11.  Burettes,  two  with  stand,  25  cc.  each,  by  1/10  cc.  for  f0 
sodium   hydroxid  (NaOH)  and   hydrochloric  acid    (HC1),  to  be 
used  in  titrating  media. 


122 


WATER   PURIFICATION   PLANTS 


12.  One  6-inch  glass  funnel,  one  4-inch  glass  funnel,  and  a  two- 
ring  retort  stand,  for  filtering  media. 

13.  18 — 250  cc.  wide-mouthed,  glass-stoppered  bottles  for  col- 
lecting samples. 

14.  6 — 250-cc.  Erlenmyer  flasks,  for  storing  media. 

15.  150 — Bacteriological  test  tubes,  %  inch  by  6  inches. 


Courtesy  Scientific  Materials  Company,  Pittsburgh,  Pa. 

FIG.  68c. — Incubator  (Water  Jacketed,  Electrically  Controlled, 
Suitable  for  20°  C.  Counts). 

16.  50 — Fermentation  tubes. 

17.  100 — Petri  dishes,  10  cm.  (4  inches)  in  diameter. 

18.  24 — 1-cc.  pipettes. 

19.  2 — 5-cc.  pipettes. 

20.  12— 10-cc.  pipettes. 

21.  Thermometer,  0°-100°  Centigrade. 

22.  Filter  paper — special  agar. 

23.  Non-absorbent  cotton,  for  plugging  test  tubes. 
Cleaning  Apparatus.     For  cleaning  new  and  used  glassware  a 

stock  solution  of  cleaning  fluid  of  the  following  proportions  should 
be  prepared: 


BACTERIAL    TESTS  123 

Sulphuric  acid,  H2SC>4  3  parts 

Potassium  bichromate,  K2Cr207  3  parts 

Water  25  parts 

This  stock  solution  is  too  strong  for  use,  it  being  customary  to 
dilute  one  part  of  it  with  twenty  of  water.  Fill  a  large  glass  jar 
with  this  dilution,  and  clean  flasks,  test  tubes,  fermentation  tubes, 
Petri  dishes,  and  pipettes  by  immersing  them  in  this  fluid,  rinsing 
them  thoroughly  under  the  tap,  and  drying  in  the  dry  sterilizer 
for  twenty  minutes. 

Preparing  Apparatus.  After  being  cleaned  as  above,  the  ap- 
paratus is  prepared  for  use  as  follows: 

The  sampling  bottles  should  be  stoppered,  wrapped  in  paper, 
and  sterilized  in  the  dry  sterilizer  for  two  hours  at  150°  C. 
They  are  then  ready  for  use  and  should  be  carefully  handled  to 
prevent  contamination. 

The  flasks  and  test  tubes  should  be  plugged  with  cotton,  the 
cotton  plug  being  large  enough  to  completely  fill  the  neck  of  the 
tube  or  flask  for  a  distance  of  three  quarters  of  an  inch,  and  should 
seat  firmly  enough  to  sustain  the  weight  of  the  tube  or  flask. 
They  are  then  sterilized  in  the  dry  sterilizer  for  two  hours  at  150° 
C.,  at  which  temperature  the  cotton  plugs  should  brown  slightly. 

The  fermentation  tubes  are  plugged  and  sterilized  in  the  same 
manner.  The  Petri  dishes  are  closed  before  sterilization  and  are 
conveniently  placed  in  wire  baskets.  The  pipettes  are  wrapped 
in  bunches  of  about  a  half  dozen,  to  prevent  contamination  of  the 
tips,  and  sterilized  as  before  mentioned. 

Preparation  of  Media.     Nutrient  Gelatin  (used  for  20°  count) : 

1.  Weigh  saucepan  and  note  weight. 

2.  Add  1000  grams  of  distilled  water  to  the  pan. 

3.  Dissolve  3  grams    of  Liebig's  beef  extract  and  10  grams  of 
pepton  (Witte's)  in  the  water,  and  heat  on  gas  stove  over  asbestos 
plate,  keeping  below  60°  C.  and  stirring  constantly. 

4.  Add  120  grams  of  best  French  gelatin,  warming  and  stirring 
constantly  until  it  is  dissolved. 

5.  Add  sufficient  distilled  water  to  make  up  to  1000  grams  and 
adjust  the  reaction  in  the  following  manner:  Pour  45  cc.  of  distilled 
water  (neutral  to  phenolphthalein)  into  an  evaporating  dish  and 
add  5  cc.  of  the  broth  with  a  pipette.     Place  the  dish  over  a 
microburner  and  boil  several  minutes  to  remove  CO2,  then  add 
1  cc.  phenolphthalein  solution  and  titrate  with  f-Q  sodium  hydroxid 


124 


WATER   PURIFICATION   PLANTS 


until  a  faint  permanent  pink  color  is  produced.  To  make  the 
reaction  of  the  broth  1  per  cent  acid,  add  normal  sodium  hydroxid 
to  the  extent  of  10  cc.  less  than  10  times  the  burette  reading. 
Should  the  broth  be  alkaline,  titrate  with  f-0  hydrochloric  acid  and 
add  normal  hydrochloric  acid  to  the  extent  of  10  cc.  more  than 

10  times  the  burette  reading. 
After  adding  the  acid,  stir  well 
to  mix  it  thoroughly. 

6.  Dissolve  the  whites  of  two 
eggs  in  50  cc.  distilled  water,  and 
after  cooling  the   gelatin  below 
60°  C.,   mix  this   solution  with 
the  gelatin  and  heat  slowly  over 
an  asbestos  plate,  stirring  con- 
stantly until  the  eggs  coagulate. 
Finish  by  boiling  the  gelatin  15 
minutes.     This  will  remove  any 
impurities  from  the  gelatin. 

7.  Adjust    weight     to     1000 
grams,  bring  to   boil,  and   filter 
while  hot.     The  arrangement  for 
filtering  and  tubing  are   shown 
in    Fig.   69.     Agar   filter    paper 
should  be  used,  and  this  and  the 
two  glass   funnels,   tubing,    and 
pipette  should  be  heated  by  run- 
ning hot  water  through  the  filter 

preliminary  to  the  gelatin.  The  gelatin  can  be  filtered  directly 
into  clean,  sterilized  test  tubes,  10  cc.  per  tube,  by  means  of  the 
pipette  attached  to  the  lower  funnel,  using  care  not  to  smear  the 
mouth  of  the  tube.  Any  surplus  can  be  run  into  Erlenmyer  flasks 
for  future  use.  Reinsert  the  cotton  plugs  in  the  tubes  and  flasks 
and  chill  by  setting  in  cold  tap  or  ice  water.  Sterilize  in  the  auto- 
clave 5  minutes  at  120°  C.  Store  in  ice  box  in  a  moist  atmos- 
phere to  prevent  evaporation.  (Keep  a  pan  of  water  in  the  ice 
box  to  keep  the  air  moist.) 

Lactose  Agar  (used  for  37°  count  and  acid-forming  bacteria): 
1.  Measure  1000  grams  of  distilled  water  into  a  weighed  sauce- 
pan and  add  15  grams  of  agar,  which  has  been  previously  cut  and 
shredded. 


FIG. 


). — Device  for  Filtering 
Media. 


BACTERIAL    TESTS 


125 


2.  Bring  to  boiling  and  boil  until  agar  is  dissolved,  stirring 
constantly  and  avoiding  violent  ebullition. 

3.  Cool  to  60°  C.  and  add  3  grams  beef  extract  and  20  grams  of 
pepton  (Witte's).     When  these  are  dissolved,  boil  5  minutes  and 
make  up  to  1000  grams  with  distilled  water. 

4.  Titrate  sample  as  for  gelatin  and  adjust  reaction  of  the  agar 


Syphon 


Glass  Funnel 

1-7 

lot  Water 
n  Funnel 


FIG.  69a. — Device  for  Heating  Agar  Filter. 

This  consists  of  a  tin  funnel,  closed  with  a  perforated  cork  into  which  the 
glass  funnel  fits.  A  glass  drain  tube  passes  through  another  hole  in  this  cork. 
This  tube  is  drawn  out  to  a  small  opening,  so  that  the  funnel  will  drain  slowly, 
and  fits  into  a  rubber  tube  leading  to  a  waste  pan.  Hot  water  is  fed  to  the 
funnel  through  a  siphon  from  a  pot  of  boiling  water.  The  tip  of  the  glass 
siphon  is  drawn  out  fine  to  regulate  the  flow.  This  device  saves  much  time 
in  filtering. 

broth  by  adding  normal  sodium  hydroxid  or  hydrochloric  acid  to 
the  extent  of  10  times  the  burette  reading  and  mixing  well. 

5.  Cool  to  60°  C.  and  add  the  whites  of  two  eggs  dissolved  in 
50  cc.  distilled  water. 

6.  Warm   slowly   until   eggs   coagulate,   finishing  by   boiling 
vigorously  over  the  free  flame  for  10  minutes.     Then  allow  to 
stand  at  a  simmering  heat  for  20  minutes. 


126  WATER    PURIFICATION    PLANTS 

7.  Make  up  to  1000  cc.  with  distilled  water  and  bring  to  a 
boil. 

8.  Filter  through  one  layer  of  cotton  flannel  (placed  in  a  glass 
funnel)  into  a  clean  saucepan. 

9.  Bring  to  boiling  point,  remove  from  flame,  and  add   10 
grams  of  chemically  pure  lactose,  mixing  thoroughly. 

10.  Filter  through  agar  paper,  as  for  gelatin,  or  better  use 
device  shown  in  Fig.  69a. 

11.  Tube,  10  cc.  per  tube,  replace  plugs,  and  sterilize  in  stream- 
ing steam  for  30  minutes  on  three  successive  days.     Keep  at 
room    temperature    between    sterilizations.     Store    in    a    moist 
chamber  or  in  an  ice  box. 

Dextrose  Broth  (for  Coli  test  in  fermentation  tubes): 

1.  Measure  1000  grams  of  distilled  water  into  a  weighed  sauce- 
pan and  add  3  grams  of  beef  extract  and  10  grams  of  pep  ton 
(Witte's) ;  when  dissolved  boil  several  minutes,  stirring  constantly, 
and  make  up  to  1000  grams. 

2.  Titrate  and  adjust  reaction  as  for  gelatin,  adding  normal 
sodium  hydroxid  or  hydrochloric  acid  to  the  extent  of  10  times 
the  burette  reading. 

3.  Clear  with  eggs  as  for  agar,  and  boil  10  minutes,  simmer 
20  minutes. 

4.  Adjust  weight  to  1000  grams,  bring  to  boiling,  and  filter  as 
for  gelatin. 

5.  Add  10  grams  of  dextrose,  mix  thoroughly,  and  tube  into 
fermentation  tubes,  completely  filling  the  arm  and  lower  one- 
fourth  of  bulb  of  tube.     Replace  cotton  plugs. 

6.  Sterilize  in  the  streaming  steam  for  thirty  minutes  on  three 
successive  days,  keeping  at  room  temperature    between    sterili- 
zations. 

Lactose  Bile  (for  Coli  test  in  fermentation  tubes) :  Dissolve  1 
per  cent  lactose  and  1  per  cent  pepton  in  fresh  ox  gall,  filter,  and 
fill  in  fermentation  tubes.  Sterilize  in  streaming  steam  for  thirty 
minutes  on  three  successive  days. 

Alternative  Method.  Add  10  per  cent  fresh  dried  ox  gall  and 
1  per  cent  Witte's  pepton  to  distilled  water  and  stir  till  dissolved. 
Fill  into  sterilized  Erlenmyer  flasks  and  heat  by  setting  flasks  in  a 
pan  of  boiling  water.  Boil  in  this  manner  for  30  minutes.  Set 
aside  over  night.  Filter  through  agar  filter  paper,  add  1  per  cent 
lactose,  and  fill  into  sterilized  fermentation  tubes.  Plug  tubes 


BACTERIAL    TESTS  127 

and  sterilize  in  streaming  steam  for  30  minutes  on  three  successive 
days. 

Litmus  Solution  (for  lactose  agar  plates):  Dissolve  1  part  of 
Merck's  pure  extract  of  litmus  in  100  parts  of  distilled  water, 
filter  and  run  into  tubes  (5  cc.  per  tube),  reinsert  cotton  plugs,  and 
sterilize  in  autoclave  5  minutes  at  120°. 

Distilled  Water  (for  dilutions):  Measure  9  cc.  of  distilled 
water  into  clean  sterilized  test  tubes,  reinsert  cotton  plugs,  and 
sterilize  in  autoclave  5  minutes  at  120°. 

Notes  on  Preparing  Media.  It  is  often  well  to  titrate  the  media 
again  after  filtering  and  before  tubing  and  to  readjust  the  reaction 
if  necessary. 

The  first  part  of  the?medla  coming  through  the  filter  is  often 
mixed  with  the  hot  water  used  in  heating  and  moistening  the  filter 
paper  and  funnels.  The  first  few  tubes  of  media  should  therefore 
be  discarded.  The  number  to  be  discarded  can  best  be  judged 
after  the  medium  is  all  tubed  and  cooled,  when  the  defective  ones 
will  be  of  a  pale  color  and  not  properly  jelled. 

There  is  often  difficulty  in  filtering  agar,  due  to  chilling  on 
the  filter  and  to  uncoagulated  albumin  coming  through  the  filter 
(especially  with  neutral  agar).  Thorough  heating  and  simmering 
as  above  described  will  help  to  overcome  this  difficulty. 

The  above  methods  aim  at  simplicity  and  economy  of  time, 
and  differ  from  the  Standard  Methods  of  the  American  Public 
Health  Association  principally  in  the  substitution  of  beef  extract 
for  meat.  Where  time  and  facilities  allow,  the  Standard  Methods 
should  be  followed.  Lean,  chopped  or  ground  beef  should  be 
used,  one  pound  per  1000  cc.  of  medium.  It  should  be  soaked  24 
hours  in  one  liter  of  distilled  water  in  a  cool  place,  and  the  juice 
strained  off  by  squeezing  strongly  through  a  piece  of  muslin.  If 
the  temperatures,  while  making  the  medium,  are  kept  low  (at 
about  60°  C.)  until  just  before  filtering,  and  the  medium  is  then 
boiled  over  a  free  flame,  no  eggs  need  be  added,  as  the  natural 
albumins  of  the  meat  will  be  coagulated  and  will  clarify  the 
medium.  It  is,  however,  often  advisable  to  use  eggs  even  in 
making  media  from  meat. 

Collecting  Samples.  Great  care  is  necessary  in  collecting 
samples  to  get  representative  ones  and  to  prevent  contamination 
from  outside  sources.  In  collecting  samples  from  the  tap,  allow 
the  water  to  run  for  15  minutes.  In  unwrapping  and  opening 


128  WATER   PURIFICATION   PLANTS 

avoid  fingering  the  mouth  of  the  bottle.  In  filling  the  bottle  and 
replacing  the  stopper,  the  water  must  not  be  allowed  to  run  from 
the  fingers  upon  the  stopper  or  into  the  mouth  of  the  bottle.  The 
stopper  must  be  held  free  from  contact  with  any  object  while 


FIG.  70. — Apparatus  for  Bacterial  Tests. 

Note  tubes  of  sterile  distilled  water  in  basket,  agar  tubes  warming  in  water 
bath,  sterile  Petri  dishes  (those  behind  have  porous  earthenware  covers), 
fermentation  tubes,  sterile  pipettes,  and  sample  collecting  bottles. 

filling  the  bottle.  Samples  from  basins  or  reservoirs  are  generally 
taken  about  a  foot  below  the  surface,  the  bottle  pointing  against 
the  current  while  filling. 

Samples  should  be  plated  immediately  after  collection,  as  if 
allowed  to  stand  changes  in  bacterial  content  occur. 

Quantitative  Test.  Warm  four  gelatin  and  four  lactose  agar 
tubes  in  a  pot  of  water,  setting  the  tubes  vertically  in  the  pot  with 
the  water  about  half-way  up  the  tubes.  They  can  be  held  vertical 
by  means  of  a  lid  perforated  to  receive  the  tubes.  The  tem- 
perature of  the  water  must  be  kept  at  about  40°  C. 

Set  out  six  sterilized  Petri  dishes,  marking  two  of  them  1  cc., 
two  1/10  cc.,  and  two  1/100  cc.  with  a  wax  pencil.  Also  set  out 
several  tubes  of  sterilized  distilled  water,  9  cc.  per  tube. 

Shake  the  sample  of  water  thoroughly,  and  with  a  sterile 
pipette  introduce  1  cc.  of  the  sample  into  each  of  the  Petri  dishes 
marked  1  cc.,  raising  the  covers  only  far  enough  to  admit  the 


BACTERIAL    TESTS  129 

point  of  the  pipette.     With  a  sterile  pipette  introduce  1  cc.  of  the 
sample  into  one  of  the  tubes  containing  9  cc.  of  sterile  water. 


FIG.  71. — Plating  Gelatin  or  Agar. 

Mix  well  and  introduce  1  cc.  of  this  dilution  into  each  of  the  Petri 
dishes   marked   1/10  cc.     Also   put  1  cc.  of  this  dilution  into  a 


FIG.  72.— Plates  from  Incubator  Ready  to  Be  Counted. 

Each  spot  on  the  plate  is  a  colony,  developed  presumably  from  one  bac- 
terium. The  left-hand  plate  is  from  a  sample  of  polluted  river  water.  The 
right-hand  plate  is  the  same  water  after  filtration.  The  board  and  lens  are 
used  to  facilitate  counting. 

second  tube  of  sterile  water,  and,  after  mixing  thoroughly,  trans- 
fer 1  cc.  from  this  tube  into  each  of  the  Petri  dishes  marked  1/100 
cc.,  using  sterile  pipettes  throughout. 

Remove  the  gelatin  tubes  from  the  water  bath,  allow  them  to 
cool  slightly,  and  pour  the  contents  of  one  tube  into  one  each  of  the 


130  WATER    PURIFICATION    PLANTS 

Petri  dishes  marked  1  cc.,  1/10  cc.,  and  1/100  cc.,  respectively, 
flaming  the  mouth  of  the  tube  in  the  microburner  before  with- 
drawing the  plug.  As  soon  as  the  gelatin  is  introduced  into  a 
Petri  dish  tilt  and  rotate  the  dish  to  mix  the  gelatin  with  the  water 
and  distribute  it  evenly  over  the  surface,  and  set  on  a  level  place  to 
cool.  In  pouring  the  gelatin  into  a  Petri  dish,  the  cover  of  the 
latter  should  be  raised  only  sufficiently  to  admit  the  moufch  of  the 
tube,  as  per  sketch,  Fig.  71.  When  the  gelatin  has  hardened, 
place  the  Petri  dishes  in  the  20°  incubator  for  48  hours.  The  num- 
ber of  growths  or  colonies  are  then  counted,  each  colony  repre- 
senting (presumably)  1  bacterium.  In  counting,  a  piece  of  paper, 
ruled  into  squares,  placed  under  the  dish,  and  a  small  hand  lens 
are  of  great  advantage.  It  is  not  necessary  to  count  all  three 
plates.  It  is  sufficient  to  count  one  which  contains  from  100  to 
200  colonies.  Record  the  count  as  "  bacteria  per  cubic  centimeter." 
If  the  1/10  dilution  plate  is  counted,  the  count  must  be  multiplied 
by  10;  if  the  1/100  dilution  is  used,  multiply  by  100. 

To  each  of  the  three  remaining  Petri  dishes  add  1  cc.  of  sterile 
litmus  solution,  using  a  sterilized  pipette.  Then  add  to  each  dish 
the  contents  of  an  agar  tube  (warmed  to  from  40°  to  43°  C.), 
naming  the  mouth  of  the  tube  as  before,  spread  the  agar  evenly 
over  the  dish,  and  allow  it  to  harden  as  before.  Incubate  in  the 
37°  incubator  for  24  hours,  and  count  as  before.  Record  the 
count  as  "  bacteria  per  cc.  at  37°  C."  Also  examine  the  plates 
for  red  colonies,  which  denote  the  acid-forming  bacteria,  and  re- 
cord their  number  per  cubic  centimeter.  Place  agar  plates  in 
incubator  upside  down  or  use  porous  covers  (Fig.  72)  to  avoid 
liquefaction. 

Fermentation  of  Dextrose  Broth.  Heat  three  fermentation 
tubes  containing  dextrose  broth  in  the  steam  sterilizer  to  drive  off 
dissolved  oxygen.  See  that  there  are  no  bubbles  of  gas  in  the  tube, 
and  allow  to  cool.  Inoculate  with  10  cc.,  1  cc.,  and  a  cc.  of  1/10 
dilution  respectively,  using  sterilized  1-  and  10-cc.  pipettes,  and 
flaming  the  mouth  of  the  tubes  before  removing  the  cotton  plug. 
Reinsert  plugs  and  mix  by  shaking  the  tube  with  a  rotary  motion ; 
tilt  several  times  until  a  little  air  rises  into  the  tube  and  tilt  back 
until  air  is  again  expelled,  so  as  to  insure  a  uniform  mixture. 
Incubate  in  the  37°  incubator  for  48  hours.  Note  whether 
gas  has  formed  in  the  tube;  if  so,  record  the  test  as  positive. 
To  determine  the  nature  of  the  gas,  fill  the  bulb  with  a  2  per 


BACTERIAL    TESTS  131 

cent  solution  of  caustic  potash,  press  the  finger  over  the  open- 
ing of  the  bulb,  and  invert  the  fermentation  tube  so  that  the 
potash  solution  flows  into  the  end  of  the  tube  containing  the  gas. 
The  reduction  in  volume  of  gas  indicates  the  amount  of  CC>2  pres- 
ent, which  is  absorbed  by  the  potash.  The  remaining  gas  is 
probably  hydrogen  (H).  Record  the  relation  between  the  two 

TJ  O  rt 

gases    as    a  fraction  —  777;-    =   -'•   for  example;     -   is  generally 


the  "  gas  relation  "  for  B.  coli. 

Fermentation  of  Lactose  Bile.  The  procedure  with  lactose 
bile  is  the  same  as  for  dextrose  broth,  substituting  lactose  bile 
fermentation  tubes.  Record  results  for  24  and  48  hours. 

Sterilizing  Old  Cultures.  In  cleaning  Petri  dishes,  fermen- 
tation tubes,  etc.,  they  should  first  be  placed  in  the  autoclave 
and  sterilized  for  half  an  hour  to  destroy  all  colonies  of  bacteria. 
If  no  autoclave  is  available,  they  should  be  sterilized  by  thorough 
boiling. 


CHAPTER   V 

INTERPRETATION  OF  TESTS 

Taste  and  Odor.  Tastes  and  odors  are  often  caused  by  the 
presence  of  diatoms,  algae,  or  small  animalcules  in  the  water. 
These  tastes  and  odors  are  due  to  volatile  oils  given  off  by  the 
cells  of  these  growths.  A  very  small  amount  of  these  oils 
causes  a  very  appreciable  taste,  one  part  in  ten  million 
being  often  detectable.  Certain  odors  seem  to  occur  at  stated 
seasons,  some  in  spring  and  autumn,  some  in  summer,  others 
in  midwinter,  due  to  the  formation  of  minute  plant  growths 
beneath  the  ice.  Ground-  and  filtered-water  supplies  when 
stored  in  reservoirs  seem  to  be  especially  favorable  to  the 
growth  of  algae,  probably  owing  to  the  relatively  large  amount  of 
free  carbonic  acid  which  these  waters  contain.  Covering  the 
reservoirs  is  an  effective,  although  expensive,  remedy.  Treating 
the  water  with  copper  sulphate  is  also  good,  one  part  of  copper 
sulphate  to  2,000,000  of  water  destroying  lower  plant  and  animal 
life  in  from  two  to  four  days.  The  proper  amount  of  copper  sul- 
phate is  placed  in  a  gunny  sack  and  dragged  back  and  forth 
through  the  water  until  it  is  dissolved.  Aerators  at  the  inlet  to 
the  basin,  and  the  chemical  treatment  of  the  water  at  the  filter 
plant  so  as  to  prevent  the  increase  in  CO 2,  also  help. 

Dissolved  gases  such  as  hydrogen  sulphid  (H2S)  and  marsh 
gas  (CH4)  cause  disagreeable  odors  which  can  be  removed  by 
aeration.  Odors  often  result  from  decomposing  organic  matter, 
especially  when  the  gases  due  to  decomposition  are  confined  under 
ice  in  winter. 

Most  of  the  above  tastes  and  odors  can  be  removed  by  aera- 
tion, followed  by  sedimentation  and  filtration,  although  swamp 
waters  sometimes  have  tastes  which  cannot  be  wholly  removed. 

Certain  minerals  cause  tastes.  Small  amounts  of  oxygen, 
carbonic  acid,  salt,  etc.,  give  water  a  pleasant  taste;  their  absence 
is  noted  in  the  "  dead  "  taste  of  artificially  distilled  water.  Salt 
in  excess  of  250  parts  per  million  of  chlorine,  causes  a  distinctly 
briny  taste.  Iron  is  noticeable  when  it  exceeds  two  parts  per 

132 


INTERPRETATION    OF   TESTS  133 

million,  and  a  high  content  of  carbonates  of  lime  and  magnesium 
imparts  a  distinct  flavor  and  an  apparent  "  heaviness  "  to  the 
water. 

Hypochlorite  of  lime,  when  used  for  sterilizing  water,  imparts 
to  it  a  taste  and  odor,  especially  when  more  than  6  to  8  pounds  per 
million  gallons  are  used.  It  is  especially  noted  in  hot  water,  a 
fact  which  is  true  of  most  tastes  and  odors. 

Turbidity.  Turbidity  is  caused  by  the  sediment  which  the 
surface  runoff  washes  from  the  land  and  which  is  carried  in  sus- 
pension in  the  stream  or  river.  Naturally  it  is  highest  during  a 
flood,  and  an  observer  acquainted  with  the  geology  of  a  river  basin 
can  tell  from  the  color  and  appearance  of  the  turbidity  in  what 
part  of  the  basin  the  rainfall  causing  the  flood  occurred.  The 
turbidity  is  composed  of  fine  particles  of  silica  or  sand  and  of  clay. 
It  is  expressed  most  conveniently  as  parts  per  million  of  silica,  al- 
though this  does  not  express  correctly  the  amount  of  suspended 

Suspended  matter  . 
matter.      The  ratio,  -    —= — 7-77 ,  is  called  the  "  Turbidity 

Coefficient,"  which  generally  runs  from  0.4  to  0.6,  but  in- 
creases with  coarse  sediment  and  decreases  with  fine.  In  alkaline 
waters  (those  containing  carbonates  or  hydroxids  of  sodium  and 
potassuim)  silica  and  alumina  often  occur  in  a  minutely  divided 
or  colloidal  state,  giving  the  water  a  smoky  appearance,  a  form  of 
turbidity  very  difficult  to  remove. 

Turbidity  is  very  significant  in  indicating  the  amount  of 
chemical  required  for  coagulation,  as  shown  by  Plates  III  and  VI. 

Filtered  water  should  show  no  turbidity  whatever,  and  in  any 
drinking  water  a  turbidity  of  5  or  over  will  cause  unfavorable 
comment. 

Color.  Color  is  due  to  vegetable  tannates  and  gallates,  re- 
sulting from  infusions  of  the  leaves  and  bark  of  decaying  vegeta- 
tion, or  to  iron  carried  in  solution  in  the  form  of  acid  carbonates 
and  sulphates,  often  combined  with  organic  matter.  Swamp  water 
is  highly  colored,  due  to  the  presence  of  decaying  vegetation,  peat 
and  muck,  and  the  prolonged  contact  of  these  with  the  water. 

Waters  containing  turbidity  due  to  clay  generally  have  very 
low  color,  after  the  turbidity  is  removed,  as  the  clay  present 
in  the  colloidal  state  has  the  power  of  removing  coloring  matter 
from  the  water  by  a  process  known  as  "  adsorption."  For  this 


134  WATER    PURIFICATION    PLANTS 

reason  the  turbid  waters  of  the  Mississippi  Valley  are  practically 
colorless,  while  the  clear  mountain  streams  of  New  England  are 
often  very  high  in  color. 

Acid  waters  of  swampy  origin  often  have  a  black  tinge,  as  the 
acids  in  combination  with  the  tannates  and  gallates  present  form  a 
natural  ink.  Iron  sulphate  gives  to  water  a  yellow  cast,  and  waters 
containing  iron  carbonates  held  in  solution  by  CO2  acquire  a 
very  fine  yellow  turbidity  when  the  CC>2  escapes,  which  is  very 
persistent. 

Color  is  undesirable,  owing  to  the  unpleasant  appearance  it 
gives  a  water,  and  to  the  fact  that  it  stains  linen  and  vegetables, 
and,  in  the  case  of  iron,  enamel  ware  and  glass.  Often  irregularity 
in  the  behavior  of  coagulants,  or  the  failure  of  coagulation,  has 
been  noticed  with  high  color,  but  the  reason  is  not  yet  well  under- 
stood.* The  maximum  color  in  a  filtered  water  should  be  less 
than  10  parts  per  million.  The  color  will  be  found  to  decrease 
during  floods,  owing  to  the  greater  dilution  of  the  water,  but  it 
sometimes  happens  that  a  river  has  a  swampy  tributary,  a  flood 
on  whose  basin  will  flush  out  the  swamps  and  cause  a  temporary 
rise  in  color. 

To  remove  color,  the  best  results  are  obtained  by  coagulation 
with  alum,  and  filtration.  It  requires  about  1  grain  per  gallon  of 
alum  to  effect  a  color  reduction  of  10  parts  per  million,  but  there 
seems  to  be  a  residuum  which  is  very  difficult  to  remove,  requiring 
3  or  4  grains  for  each  10  parts  of  color.  The  portion  so  difficult  to 
remove  is  probably  in  true  solution,  the  other  being  present  as  a 
colloidal  solution. 

Alkalinity.  Alkalinity  is  the  property  of  a  water  due  to  the 
presence  of  hydroxyl  ions.  It  is  caused  by  the  hydroxids  and  car- 
bonates of  the  alkalis  (sodium  and  potassium) ,  and  by  the  hydrox- 
ids, carbonates,  and  bicarbonates  of  the  alkaline  earths  (calcium, 
magnesium,  and  [occasionally]  lithium) .  Of  these  the  hydroxids  of 
calcium  and  magnesium  are  found  only  in  filter  effluents  (through 
improper  operation),  and  the  hydroxids  of  sodium  and  potassium 
in  waters  of  the  Far  West.  Carbonates  of  soda  are  common  in 
many  waters,  and  bicarbonates  of  calcium  and  magnesium  are 
almost  universally  present  and  in  the  majority  of  waters  con- 

*  It  is  thought  that  the  coloring  matter  forms  films  about  the  minute  par- 
ticles of  incipient  coagulum  and  prevents  these  from  collecting  into  sizable 
clots. 


INTERPRETATION    OF   TESTS  135 

stitute  at  least  fifty  per  cent  of  the  mineral  matter  in  solution. 
Calcium  and  magnesium  carbonates  are  only  slightly  soluble,  and 
are  therefore  found  in  small  quantities  only.  If  carbonic  acid  is 
present  it  combines  with  the  carbonates  to  form  the  highly 
soluble  bicarbonates  of  calcium  and  magnesium. 

It  is  a  common  mistake  to  assume  that  alkalinity  and  "  hard- 
ness "  are  the  same,  for  this  can  only  be  true  when  all  the  alkalinity 
is  due  to  bicarbonates  of  calcium  and  magnesium.  These  con- 
stitute "  temporary  hardness,"  so  called  from  the  fact  that  they 
are  precipitated  by  heating  the  water,  as  the  carbonic  acid  holding 
them  involution  is  then  driven  off.  The  sulphates,  chlorids,  and 
nitrates  of  calcium  and  magnesium  do  not  contribute  to  the 
alkalinity  of  a  water,  yet  they  cause  "  permanent  hardness,"  not 
being  precipitated  by  ordinary  boiling,  although  if  boiled  under 
pressure,  as  in  generating  steam  for  power  purposes,  they  pre- 
cipitate and  form  a  hard  scale  in  the  boiler.  Mineral  acids  also 
cause  hardness. 

Popularly  any  water  with  which  it  is  difficult  to  obtain  a  soap 
lather  is  termed  "  hard."  This  difficulty  arises  .from  the  fact 
that  the  salts  of  calcium  and  magnesium  (and,  to  a  small  extent, 
of  iron,  lithium,  and  zinc)  form  insoluble  salts  with  soaps,  which 
form  a  scum  on  the  sides  of  the  containing  vessel,  and  until  the 
calcium  and  magnesium  salts  are  thus  precipitated  no  lather  re- 
sults. Taking  sodium  stearate  (NaCi8H3502)  as  a  type  of  soap, 
the  reactions  are  as  follows  : 

For  temporary  hardness: 
N 
For  permanent  hardness: 


Alkalinity  finds  a  practical  use  in  water  purification  by  its 
reaction  with  alum  (aluminum  sulphate)  to  form  a  coagulant,  as  is 
more  fully  explained  in  Chapter  VI,  and  diagrammed  on  Plates 
IV  and  V. 

Potable  waters  should  be  alkaline  at  all  times  to  the  extent 
of  at  least  10  parts  per  million,  and  a  maximum  alkalinity  of  not 
over  75  is  desirable  in  water  supplies,  to  limit  the  sbap  consuming 
powers.  For  boiler-feed  purposes  an  alkalinity  of  100  or  less  gives 
very  little  trouble  because  of  soft  scale. 


136  WATER   PURIFICATION    PLANTS 

Acidity.  This  test  as  usually  run  with  erythrosin  indicates 
the  acidity  due  to  free  sulphuric  acid  and  the  sulphates  of  iron  and 
aluminum.  By  using  methyl  orange  as  an  indicator,  sulphuric 
acid  only  is  indicated.  The  correction  of  acidity  with  lime  and 
soda  ash  is  shown  on  Plates  IV  and  V,  and  explained  in  Chapter 
VI.  Acid  waters  attack  plumbing  fixtures,  piping,  boilers,  and 
even  the  cast-iron  impellers  of  centrifugal  pumps  and  the  interior 
passages  of  plunger  pumps.  Ferrous  sulphate,  in  particular,  at- 
tacks wrought  iron  vigorously.  Acid  waters  will  destroy  patho- 
genic bacteria  such  as  B.  coli,  B.  typhosus,  and  vegetative  forms, 
and  such  waters  often  seem  quite  sterile.  Many  bacteria,  however, 
form  "  spores  "  under  adverse  conditions  and  become  active  again 
after  the  water  is  rendered  alkaline  by  the  lime  or  soda  ash  used  in 
coagulation,  often  to  the  surprise  of  the  operator,  the  raw-water 
counts  being  zero  and  the  settled-water  counts  very  high. 

Free  CO2.  Carbonic  acid  is  acquired  by  water  in  its  passage 
through  the  air  and  over  and  through  the  surface  soil,  being  a 
product  of  the  decay  and  fermentation  of  vegetable  and  animal 
matter.  It  is  generally  present  during,  or  increased  by,  a  rising 
river,  due  to  bayous,  swamps,  etc.,  containing  stagnant  water  and 
decaying  vegetation,  being  flushed  out.  The  indication  of  other 
acids  by  this  test  and  the  correction  to  be  made  for  such  conditions 
have  been  pointed  out. 

The  faculty  of  CO2  for  rendering  the  almost  insoluble  carbon- 
ates of  calcium,  magnesium,  and  iron  soluble  by  entering  into 
combination  with  them  has  been  remarked.  The  combination 
does  not  seem  to  be  a  truly  chemical  one,  as  the  CO2  is  readily 
driven  off  and  the  normal  carbonates  precipitated,  in  the  case  of 
calcium  and  magnesium,  by  heating,  and,  in  the  case  of  iron  car- 
bonates, by  merely  agitating  or  aerating  the  water.  These  bicar- 
bonates  are  therefore  generally  indicated  by  chemical  formulas  as 
follows:  CaCO3,H2C03;  MgC03,  H2C03;  and  FeCO3,  H2C03,  the 
commas  indicating  a  loose  or  temporary  type  of  combination. 

The  presence  of  free  carbonic  acid  renders  a  water  more  favor- 
able to  the  growth  of  algae  and  vegetable  forms,  it  being  an  im- 
portant source  of  food  supply  for  plants. 

In  iron-lime  coagulation,  the  C02  must  be  removed  either  by 
the  addition  of  sufficiently  more  lime  (above  that  required  to  react 
with  the  iron  sulphate),  or  by  aeration.  The  latter  is  generally 
the  cheaper,  but  to  be  effective  the  contact  of  the  air  with  the 


INTERPRETATION   OF   TESTS  137 

water  must  be  intimate.  Water  falling  in  thin  sheets  is  not  very 
effectively  aerated,  but  by  making  it  fall  over  successive  steps, 
being  broken  into  drops  at  each  step,  due  to  the  splashing,  it  is 
possible  to  remove  dissolved  gases  at  the  rate  of  10  parts  per 
million  per  second  of  exposure  in  summer,  and  about  half  that 
amount  in  winter.  Where  aerators  are  used,  free  CO2  determina- 
tions should  be  made  before  and  after  aeration  to  determine  the 
reduction,  and  the  amount  of  lime  used  should  be  such  as  to 
remove  the  free  CO2  left  after  aeration. 

Aside  from  its  effect  on  the  process  of  coagulation,  free  CC>2  has 
a  very  decided  corrosive  action  on  service  pipes.  This  corrosive 
action  is  much  more  pronounced  in  the  case  of  soft  water  than  of 
hard,  as  the  latter  forms  a  protective  coating  of  calcium  car- 
bonate on  the  inside  surface  of  the  pipe.  For  this  reason  a  small 
amount  of  C02  (5  parts  per  million  or  less)  is  sometimes  allowable 
in  a  hard  water,  not  subject  to  marked  decreases  in  alkalinity 
during  floods,  if  it  can  be  proven  that  there  is  no  corrosive  action 
on  pipes.  Lead  pipe  is  most  easily  dissolved,  and  as  the  lead  re- 
mains in  solution  in  the  water  and  is  a  cumulative  poison,  the  use 
of  a  water,  rendered  corrosive  by  C02,  is  dangerous  in  such  a  pipe, 
J^  part  per  million  of  lead  being  considered  the  danger  limit. 
Free  C02  also  dissolves  and  holds  in  solution  zinc  from  the  coating 
of  galvanized  pipe,  this  being  injurious  to  health,  but  not  so  dan- 
gerous as  lead,  zinc  not  being  cumulative  (i.e.,  not  remaining  in  the 
system).  Copper  is  also  dissolved  from  brass  pipe  and  is  often  a 
source  of  complaint,  as  when  soap  is  added  to  the  water  (es- 
pecially if  it  is  very  clear)  a  blue  tinge  results,  owing  to  the  re- 
action between  the  copper  and  the  ammonia  in  the  soap. 

Water  after  treatment  is  free  from  carbonic  acid  if  it  reacts 
pink  with  phenolphthalein  on  addition  of  a  drop  of  -§$•  sodium  car- 
bonate. The  proper  amounts  of  soda  and  lime  to  use  in  removing 
carbonic  acid  is  taken  up  in  connection  with  coagulation  (Chapter 
VI),  and  is  shown  on  the  diagrams,  Plates  IV,  V,  and  VII. 

Iron.  Iron  is  present  in  water  in  the  form  of  carbonate,  ferric 
sulphate,  and  ferrous  sulphate.  Most  sands,  gravels,  and  rocks 
contain  iron  in  the  form  of  the  oxid  (Fe2O3).  Water  containing 
organic  matter,  coming  in  contact  with  this  iron  oxid  in  its  passage 
through  the  ground,  deprives  it  of  oxygen,  in  order  to  oxidize  the 
organic  matter  it  contains,  reducing  the  ferric  oxid  (Fe2O3)  to 
ferrous  oxid  (FeO).  The  latter  is  combined  with  the  carbonic  acid 


138  WATER   PURIFICATION   PLANTS 

present  in  the  water  to  form  ferrous  bicarbonate,  which  is  carried  in 
solution.  Wells  drilled  near  a  polluted  river  are  generally  high  in 
ferrous  carbonates,  and  ground  water  supplies  from  subterranean 
gravel  deposits  may  or  may  not  be  high  in  iron.  The  amount 
of  iron  in  a  water  fluctuates,  but  if  once  present  is  not  likely  to  de- 
crease with  consumption.  Iron-containing  waters  are  often  clear 
when  first  pumped  from  the  ground,  but  on  standing  a  brown 
turbidity  appears,  as  the  water  absorbs  oxygen  from  the  air,  and  as 
the  carbonic  acid  in  the  water  escapes. 

Waters  containing  more  than  0.5  part  per  million  of  iron  are 
objectionable  for  domestic  use,  owing  to  the  astringent  taste,  the 
discoloring  of  linen  and  porcelain,  and  the  deposits  of  iron  oxid  in 
the  mains,  as  the  soluble  carbonate  oxidizes,  which  deposits  ap- 
pear at  the  faucets  whenever  the  water  in  the  mains  is  stirred  up 
(as  during  a  fire) .  A  fungus,  Crenothrix  polyspora,  grows  in  iron- 
containing  waters,  using  the  soluble  iron  in  its  life  processes.  As 
this  organism  requires  no  light,  it  will  grow  in  the  water  mains, 
causing  a  disagreeable  taste  and  odor,  and,  after  its  death,  the 
sheath  remains  in  the  water  as  a  brown,  gelatinous  precipitate. 

Iron  sulphate,  both  ferrous  and  ferric,  is  often  present  in  water 
containing  coal-mine  drainage,  and  when  held  in  solution  by,  or 
combined  with,  carbonic  or  organic  acids,  or  with  colloidal  matter 
is  most  difficult  to  remove.  It  is  present  if  the  water  tested  shows 
iron  and  mineral  acidity  with  erythrosin.  Practically  1  part  per 
million  of  iron  combines  with  3  parts  of  mineral  acidity  as  H2SO4 
to  give  4  parts  per  million  ferric  sulphate.  The  amount  of  mineral 
acidity  used  in  this  way  cannot  be  greater  than  the  difference  be- 
tween the  acidity  with  erythrosin  and  with  methyl  orange,  and 
is  less  if  aluminum  sulphate  is  present.  Iron  sulphate  has  a 
practical  use  in  coagulation,  as  the  addition  of  lime  causes  coagula- 
tion to  take  place.  This  will  be  further  taken  up  in  Chapter  VI. 

Aeration  is  very  valuable  in  removing  soluble  iron  from  ground 
water  and  should  be  followed  by  sedimentation  and  filtration  to 
remove  the  precipitated  oxid.  Sometimes  a  satisfactory  removal 
cannot  be  accomplished  in  this  way,  and  the  use  of  lime  and  alum 
must  be  resorted  to. 

The  sulphate  in  mine  waters  is  generally  in  both  ferrous  and 
ferric  form,  but  if  the  water  is  high  in  organic  matter  or  for  any 
other  reason  is  devoid  of  oxygen,  it  may  be  entirely  in  the  ferrous 
condition.  The  removal  is  accomplished  as  follows:  To  the  raw 


INTERPRETATION    OF   TESTS  139 

water  add  enough  lime,  a,  to  neutralize  the  free  CO2  present  after 
aeration  (1  grain  of  lime  per  gallon  to  each  12  parts  per  million 
CO2);  b,  to  precipitate  the  iron  sulphate  as  ferric  hydroxid  (re- 
quiring 1  grain  of  lime  per  gallon  to  each  35  parts  per  million  of 
ferric  sulphate);  c,  to  provide  an  excess  of  lime  of  %  grain  per 
gallon.  If  the  water  contains  dissolved  or  colloidal  organic  matter 
or  manganese  it  may  be  necessary  to  increase  the  amount  of  lime 
or  even  to  add  a  coagulant.  Aerate  the  water  at  entrance  to 
settling  basin,  and  allow  from  4  to  12  hours  for  sedimentation.  A 
long  period  of  sedimentation  is  necessary  in  iron  removal,  other- 
wise iron  and  calcium  carbonate  deposits  will  form  in  the  filters. 
Sedimentation  should  be  followed  by  filtration  in  the  usual  manner. 

Free  Alum  (A12(SO4)3)  in  the  Effluent.  The  logwood  test 
gives  indication  of  the  presence  of  aluminum  sulphate  in  the  filtered 
water,  due  to  incomplete  reaction  with  the  alkalinity  or  lime 
added  to  the  raw  water,  and  the  consequent  passing  of  the  alum 
through  the  filters  in  solution.  This  test  is  very  delicate,  but  is 
sometimes  affected  by  abnormal  conditions  of  the  raw  water.  The 
running  of  a  blank  known  to  contain  aluminum  sulphate  prac- 
tically eliminates  any  uncertainty.  As  a  check,  test  the  filtered 
water  for  alkalinity  with  erythrosin.  An  alkaline  reaction  proves 
that  no  alum  is  present,  while  an  acid  reaction  shows  the  presence 
of  alum.  Should  the  logwood  test  indicate  the  presence  of  alum, 
while  the  filtrate  is  alkaline  to  erythrosin,  it  is  highly  probable 
that  minute  particles  of  aluminum  hydroxid  are  coming  through 
the  filter  in  a  colloidal  form,  due  either  to  the  sand  being  too  coarse, 
the  "  mat  "  on  the  filter  being  too  thin,  or  too  much  lime  or  soda 
ash,  or  too  little  alum  (if  the  coagulation  is  poor)  being  used. 

It  is  very  important  that  no  free  aluminum  sulphate  be  al- 
lowed to  get  into  the  filtered  water,  owing  to  its  corrosive  and 
(to  a  small  extent)  physiological  effects.  Positive  tests  in  the  fil- 
trate maybe  due:  a, most  often  to  not  enough  lime  or  soda  ash  being 
used  to  combine  with  the  alum  in  a  water  of  low  alkalinity;  b,  to 
the  filter  beds  being  cracked  or  dirty,  if  the  settled  water  is  alkaline 
to  erythrosin;  c,  to  the  use  of  too  much  lime  or,  more  often,  soda 
ash,  with  a  turbid  river  water.  When  the  filtered  water  is  acid  to 
erythrosin,  and  the  logwood  test  indicates  free  alum,  lime  or 
soda  ash  should  be  increased  so  that  the  filtrate  has  a  minimum 
alkalinity  of  10  parts  per  million.  If  the  filtered  water  is  alkaline 
to  erythrosin,  and  sufficient  alkalinity  is  present  in  the  raw  water, 


140  WATER    PURIFICATION    PLANTS 

more  alum  should  be  added  and  care  should  be  used  to  keep  a 
good  unbroken  mat  on  the  filters.  Condition  "  c  "  need  cause 
no  alarm,  the  alum  present  being  derived  from  the  clay  turbidity 
of  the  raw  water,  some  of  which  is  reduced  to  the  colloidal  state 
by  the  excessive  use  of  lime  or  soda  ash.  In  the  colloidal  state 
(as  A12(OH)6)  it  is  neither  corrosive  nor  physiologically  harmful. 

Free  Iron  (FeSO4)  in  the  Effluent.  As  with  alum,  this  is  in- 
dicated by  the  logwood  test  and  verified  by  the  acidity  of  the  filtrate 
to  erythrosin.  The  remedies  are  to  increase  the  amount  of  lime 
used  so  that  the  settled  water  gives  a  faint  pink  reaction  with 
phenolphthalein  and  to  wash  the  filters. 

Bacteria.  While  turbidity,  color,  odor,  acid,  etc.,  may  make 
a  water  objectionable  for  domestic  use,  the  real  source  of  danger 
to  health  exists  in  the  presence  of  certain  disease-producing 
bacteria — namely,  those  causing  typhoid  fever,  cholera,  dysentery, 
and  probably  some  other  diseases.  This,  coupled  with  the  fact 
that  these  organisms  (being  a  type  of  fungi)  exist  on  organic 
matter,  gives  to  their  presence  in  excessive  numbers  in  a  water 
great  significance.  Primarily,  it  points  out  the  fact  that  the 
water  contains,  or  has  recently  been  in  contact  with,  organic 
matter  (not  necessarily  in  a  decaying  state),  and,  further,  it  suggests 
the  possibility  of  pollution  by  animal  or  vegetable  refuse  and  the 
presence  of  specific  disease  bacteria.  The  bacterial  count  at  20° 
indicates  the  water  and  soil  bacteria,  the  count  at  37°  those  of 
pathogenic  or  sewage  origin.  This  division  is  not  rigid,  as  occa- 
sionally species  occur  which  grow  at  both  temperatures.  The 
ratio  of  the  37°  to  the  20°  count  is  an  index  to  the  pollution 
of  a  water.  For  pure  water  this  ratio  is  as  1  to  10  or  more,  for 
heavily  polluted  water  it  may  run  up  to  1  to  1,  or  even  more. 
The  number  of  bacteria  increases  during  freshets  due  to  the  sur- 
face water  washing  soil  bacteria  into  the  stream,  and  a  reasonable 
allowance  may  be  made  for  this  increase. 

The  presence  of  acid-forming  colonies  on  litmus  lactose  agar 

2 

and  the  fermentation  of  dextrose  broth  with  a  gas  relation  of  — 

is  taken  to  indicate  the  presence  of  B.  coli.  Bacillus  coli  is  gen- 
erally taken  as  direct  evidence  of  fecal  pollution,  and  certainly 
should  be  considered  of  great  significance,  and  if  present  with  any 
degree  of  frequency  would  justify  a  thorough  examination  of  the 


INTERPRETATION    OF   TESTS  141 

process  of  coagulating,  settling  and  filtering  being  used,  and  the 
correction  of  any  defects  found,  supplemented  if  necessary  by  the 
application  of  hypochlorite  of  lime  to  the  filtrate.  Much  stress 
cannot  be  laid  on  isolated  positive  tests,  as  the  colon  bacillus  is 
sometimes  found  far  from  possible  pollution;  other  species  some- 
times give  positive  tests,  and  certain  bacteria  interfere  with  the 
growth  of  coli,  and  by  their  presence  spoil  tests.  Lactose  bile 
fermentation,  in  addition  to  the  above  tests,  gives  quite  positive 
proof  that  coli  are  present,  this  medium  being  the  most  reliable 
known  for  the  purpose. 

The  following  may  be  taken  as  the  standard  for  the  bacterial 
content  of  a  filtered  water:  20°  C.  count  below  100  (200  maybe 
allowable  in  large  turbid  rivers) ;  few  bacteria  on  agar  at  37°  C. 
(a  1  to  10  ratio  or  better) ;  very  infrequent  p-cid-forming  bacteria 
on  litmus  lactose  agar;  coli  absent,  except  for  an  occasional  sample, 
and  then  not  numerous. 

Much  stress  is  sometimes  laid  on  the  ratio  of  bacteria  in  the 
raw  water  to  those  in  the  filtrate  (counts  at  20°  C.),  the  percentage 
of  removal  constituting  the  "  bacterial  efficiency  "  of  the  process 
of  filtration.  It  is  not  the  percentage  of  removal  that  is  important, 
but  the  number  and  kind  of  bacteria  in  the  filtered  water.  With  a 
large  number  of  bacteria  in  the  raw  water,  a  high  efficiency  may  be 
attained,  and  still  the  effluent  be  unsatisfactory  from  a  hygienic 
standpoint,  while  with  an  almost  sterile  water  a  low  "  efficiency  " 
would  be  permissible. 


CHAPTER  VI 

COAGULATION  AND  STERILIZATION 

THE  purposes  of  coagulation  are  to  collect  the  fine  suspended 
matter  in  the  water  into  clots  or  masses  of  a  size  which  will  readily 
settle  to  the  bottom  of  the  sedimentation  basins  and  to  form  a  film 
over  the  filter  sand  which  will  prevent  even  the  finest  suspended 
particles  from  passing  through.  Coagulation  also  assists  in  re- 
moving color,  odors,  and  tastes  from  the  water,  as  will  be  pres- 
ently explained. 

Description  of  the  Process.  The  process  of  coagulation  is 
based  on  the  fact  that  soluble  salts  of  aluminum,  iron  (in  both  the 
ferrous  and  ferric  state),  zinc,  copper,  and  some  other  metals 
react  with  solutions  of  the  hydroxids,  carbonates,  and  bicarbonates 
of  the  alkalis  and  alkaline  earths  to  form  gelatinous  precipitates 
of  the  hydroxids  of  the  metals.  For  economic  reasons  and  be- 
cause of  the  poisonous  qualities  of  the  salts  of  some  of  the  other 
metals,  sulphate  of  aluminum  or  sulphate  of  iron  are  most 
generally  used,  the  required  concentration  of  hydroxyl  ions  being 
supplied  by  the  salts  of  the  alkaline  earths  naturally  present  in 
water,  or,  in  the  absence  of  these  in  sufficient  quantity,  by  the 
addition  of  hydrated  lime  or  soda  ash. 

When  sulphate  of  aluminum  or  sulphate  of  iron  (under  proper 
conditions)  is  added  to  water,  the  precipitate  takes  the  form  of 
small  flakes  about  the  size  of  a  pin-head,  and  white  (with  aluminum) 
or  greenish  brown  (with  iron)  in  color.  Due  to  their  gelatinous 
form,  these  flakes  sink  very  slowly — indeed,  appear  to  the  eye  to 
be  floating  in  the  water.  As  is  commonly  the  case  with  reactions 
between  solutions  in  water,  the  precipitate  tends  to  form  about  the 
particles  of  silt,  bacteria,  etc.,  present,  and  in  traveling  through  the 
water,  more  silt  becomes  attached  to  the  flakes  of  coagulum  and 
these  unite,  one  with  the  other,  until  quite  sizable  masses  are 
formed,  which  either  settle  to  the  bottom  of  the  sedimentation 
basins,  or  are  caught  on  the  filter  sand,  being  too  large  to  pass 
through  the  interstices  between  the  grains.  Such  of  the  coagulum 
as  is  carried  over  to  the  filters  forms  a  gelatinous  coating  over  the 

142 


COAGULATION   AND   STERILIZATION  143 

surface  of,  and  in  the  upper  part  of,  the  filter  sand,  which  con- 
stitutes the  real  filtering  medium.  Without  proper  coagulation, 
filtration  at  the  high  rates  used  in  the  mechanical  process  would 
be  impossible,  and  its  advantage,  even  with  slow  sand  filters,  is 
becoming  evident,  as  it  enables  them  to  operate  at  higher  rates 
and  effects  a  more  complete  removal  of  organic  matter. 

Theory  of  Coagulation.  Recent  experiment  and  research  in 
this  and  allied  lines  of  chemistry  have  brought  to  light  some  in- 
teresting facts  regarding  coagulation.  When  aluminum  sulphate 
or  a  similar  salt  is  added  to  water  naturally  alkaline  or  rendered  so 
artificially  by  the  addition  of  lime  or  soda  ash,  a  reaction  takes 
place,  as  a  result  of  which  an  invisible  jelly-like  substance  forms 
throughout  the  water.  Supposedly  this  has  the  structure  of  a  very 
open-meshed  network  or  sponge.  Under  suitable  conditions  this 
network  contracts  and  breaks  up  into  the  flakes  of  coagulum  al- 
ready described.  This  change  is  called  flocculation  or  coagulation. 
In  the  present  case  this  flocculation  is  brought  about  by  the  pres- 
ence of  an  electrolyte,  calcium  sulphate,  which  is  one  of  the  by- 
products of  the  reaction  between  aluminum  or  iron  sulphate  and 
the  hydroxyl  ions  present  in  the  water.  It  may  also  occur  through 
the  presence  of  fine  clay  or  silica  particles  in  the  water,  by  me- 
chanical agitation  of  the  water  or  by  allowing  it  to  flow  over 
granular  or  glassy  surfaces.  The  presence  of  organic  matter  or 
vegetable  emulsions  in  the  water,  or  the  presence  of  alkalis  in 
certain  concentrations,  will  at  times  prevent  or  seriously  retard 
coagulation. 

This  network  in  contracting  will  envelope  or  entrap  particles  of 
silt,  bacteria,  etc.  The  resulting  flakes  have  a  very  fine  sponge- 
like  structure,  which  enables  them  to  absorb  coloring  matter  and 
gases  in  solution  in  the  water.  It  is  another  peculiarity  of  this 
coagulum  that  by  its  presence  clay,  silt,  organic  matter,  etc.,  which 
may  be  present  in  a  very  finely  divided  condition,  are  caused  to 
coagulate  and  precipitate. 

The  portion  of  the  coagulum  which  is  carried  over  on  to  the 
filters  forms  over  the  sand  a  film  or  layer  of  gelatinous  substance 
perforated  by  very  fine  pores,  through  which  water  readily  passes, 
but  which  are  impenetrable  to  fine  suspended  matter  or  even  to 
matter  in  pseudo-solution.  This  film  on  the  filters  also  has  an 
absorptive  action  on  the  water  passing  through  it,  removing  there- 
from coloring  matter  and  odors  or  tastes. 


144  WATER   PURIFICATION    PLANTS 

Chemicals  Used  in  Coagulation.  The  chemicals  used  in  the 
process  of  coagulation  are:  aluminum  sulphate,  iron  sulphate, 
quicklime,  hydrated  lime,  and  soda  ash.  The  properties  and' 
characteristics  of  these  chemicals,  their  use  and  their  reactions  in 
water  purification  are  described  in  the  following  paragraphs. 

Aluminum  Sulphate.  Aluminum  sulphate  (A^SO^slSH^O), 
commonly  called  "  filter  alum,"  in  its  purest  commercial  form  con- 


FIG.  73.  —  Aluminum  Sulphate  and  Coagulation. 


sists  of  small  lumps  (J^  to  2J^  inches  in  size),  hard,  having  a  greasy 
feel  and  an  opaque,  greenish-white  color.  It  should  contain  51 
per  cent  aluminum  sulphate  and  49  per  cent  water  of  hydration, 
but  owing  to  the  process  of  manufacture  the  composition  may 
vary,  and  some  authorities  assign  to  the  commercial  product  the 
formula  Al2(S04)3l6H2O.  •  Theoretically  it  should  contain  15.3 
per  cent  of  water-soluble  alumina  (A12O3),  but  it  is  generally  speci- 
fied to  contain  not  less  than  17  per  cent,  being  known  as  "  basic  " 
aluminum  sulphate.  It  should  not  contain  more  than  0.5  per 
cent  of  matter  insoluble  in  cold  distilled  water.  Impure  "  alum  " 
generally  has  a  distinct  brownish  tinge.  Aluminum  sulphate  may 
be  obtained  in  carload  lots,  or  in  barrels  which  weigh  about  380 
pounds  gross. 


COAGULATION  AND   STERILIZATION  145 

Alum  is  used  as  a  coagulant  in  conjunction  with  slaked  lime, 
soda  ash,  or  the  natural  alkalinity  of  the  raw  water.     The  chemical 
reactions  are  as  follows: 
1.  Alum  and  lime, 


2.  Alum  and  soda  ash, 

Al2(SO4)3-f3Na 

3.  Alum  and  alkalinity  (as  CaCO3,H2CO3), 


In  all  three  reactions  the  effective  coagulum  formed  is  aluminum 
hydroxid  (A12(OH)6),  which  appears  as  a  flocculent  precipitate. 
In  reactions  1  and  3,  calcium  sulphate  (CaSCX),  and  in  reaction  2, 
sodium  sulphate  (Na2SO4),  are  formed  and  remain  in  solution. 
Calcium  sulphate  causes  permanent  hardness  and  is  objectionable, 
especially  in  boiler-feed  water,  forming  a  very  hard  scale.  The 
increase  in  permanent  hardness  is  10.4  parts  per  million,  or  about 
0.6  grain  per  gallon  for  each  grain  per  gallon  of  aluminum  sulphate 
used.  The  sodium  sulphate  is  unobjectionable  in  the  amounts 
present.  In  reactions  2  and  3,  carbonic  acid  (CO2)  is  an  objection- 
able by-product,  especially  in  waters  of  low  alkalinity,  owing  to  its 
corrosive  action.  Thus  reaction  3,  most  commonly  used  because 
cheapest,  gives  an  effluent  containing  two  objectionable  con- 
stituents, and  reactions  1  and  2  an  effluent  containing  one  ob- 
jectionable constituent.  The  ideal  way,  and  the  most  expensive, 
would  be  to  use  reaction  2,  and  add  sufficient  lime  or  soda  ash  to 
neutralize  the  carbonic  acid.  This  may  be  necessary  in  treating 
waters  of  low  alkalinity  where  the  corrosive  action  of  the  carbonic 
acid  causes  trouble,  although  it  may  be  possible  to  remove  part  of 
the  CO2  by  reaeration  after  filtration.  The  carbonic  acid  also 
gives  the  water  an  increased  tendency  toward  algae  growths, 
which  often  become  abundant  when  filtered  water  is  stored  in  open 
reservoirs. 

If  sufficient  alkalinity,  natural  or  artificial,  is  not  present  to 
react  with  the  aluminum  sulphate,  basic  sulphates  will  form. 
These  are  soluble,  so  that  no  coagulation  will  appear  under  such 
conditions.  The  reactions,  using  natural  alkalinity,  are: 


2Al2(SO4)3+3CaCO3H2CO3  =  Al2(SO4)3Al2(OH)6+3CaSO4+6C02 


146  WATER   PURIFICATION   PLANTS 

Any  one  of  these  reactions  may  take  place,  depending  on  condi- 
tions. This  accounts  for  the  difficulty  of  obtaining  coagulation 
sometimes  met  with,  especially  in  winter,  when  the  reactions  are 
slow  and  the  coagulum  formed  would  combine  with  the  aluminum 
sulphate  still  in  solution.  Under  cold-weather  conditions  some  of 
the  alum  may  pass  through  the  filters  in  this  soluble  basic  form,  the 
reaction  being  completed  in  the  clear-water  basin,  causing  the 
formation  of  minute  specks  of  coagulum  in  the  filtrate.  Using 
more  lime  or  soda  ash  will  tend  to  remedy  this  condition,  which  is 
most  apt  to  occur  when,  in  addition  to  low  temperature,  the  water 
is  low  in  alkalinity. 

The  presence  of  alkalis  (sodium  and  potassium)  in  the  water 
may  cause  a  failure  to  coagulate,  the  hydroxid  forming  as  a  colloidal 
solution,  which  does  not  assist  in  clarifying  the  water  and  will  pass 
through  the  filters,  giving  the  effluent  a  smoky  appearance.  A 
decrease  in  lime  or  an  increase  in  alum  will  assist  in  overcoming 
this. 

"  Alum  "  is  very  successful  in  removing  color  caused  by  the 
tannates  and  gallates  in  swamp  water.  One  grain  per  gallon  of 
aluminum  sulphate  will  remove  about  10  parts  per  million  of  color, 
but  this  varies  with  different  waters,  the  color  being  harder  to  re- 
move in  some  cases  than  in  others.  It  also  removes  organic 
matter,  as  has  been  mentioned. 

The  amount  of  aluminum  sulphate  to  use  generally  depends  on 
the  turbidity  of  the  raw  water.  With  clear  water  a  minimum  of 
0.3  grain  per  gallon  should  always  be  used,  and  it  may  be  neces- 
sary to  increase  this  up  to  2  grains  per  gallon,  according  to  the 
pollution  of  the  stream,  which  in  this  case  governs.  With  turbid 
waters  the  suspended  clay  has  considerable  affinity  for  the  organic 
matter  which  causes  pollution,  removing  much  of  it  by  absorptive 
action,  and  the  bacterial  reduction  is  roughly  proportional  to  the 
reduction  in  turbidity,  therefore  the  latter  is  used  as  a  convenient 
measure  of  the  amount  of  coagulant  required.  As  shown  by 
Plate  III,  the  amount  of  aluminum  sulphate  required  increases 
with  the  turbidity,  but  less  is  generally  required  with  coarse 
turbidity  than  with  fine.  With  very  turbid  waters,  some  of  the 
aluminum  sulphate  and  aluminum  hydroxid  is  absorbed  by  the 
clay  in  suspension,  and  an  additional  allowance  must  be  made  for 
this.  No  two  waters  have  the  same  alum-turbidity  ratio,  and  it  is 
recommended  that  each  operator  should  determine  by  experiment 


COAGULATION   AND    STERILIZATION  147 

the  most  economic  amount  of  chemical  for  different  turbidities, 
and  plot  a  curve  on  Plate  III  covering  the  particular  case  of  the 
water  he  is  treating. 

The  final  test  for  the  proper  amount  of  aluminum  sulphate  to 
use  is  of  course  the  clarity  of,  and  bacterial  removal  in,  the  filtrate. 
The  size  of  the  flakes  of  coagulum  should  be  about  that  of  half  a 
pin-head.  If  the  coagulated  water  appears  clear  or  smoky,  with  no 
flakes  visible,  more  alum  should  be  used,  unless  the  alkalinity  is 
very  close  to  a  minimum  required  to  decompose  the  alum  being 
used,  in  which  case  add  more  lime  or  soda  ash.  The  smoky  or 
"  pin-point  "  coagulation  is  most  common  in  winter,  owing  to  the 
more  sluggish  action  of  the  chemicals.  If  the  flakes  are  large  and 
feathery,  the  amount  of  alum  should  be  decreased. 

The  aluminum  sulphate  will  react  directly  with  the  natural 
alkalinity  in  the  water  if  there  is  sufficient  of  the  latter.  Each 
grain  per  gallon  requires  for  complete  reaction  10  parts  per  million 
of  natural  alkalinity,  as  determined  by  the  erythrosin  test,  and 
there  should  be  an  excess  of  alkalinity  of  at  least  10  parts  over 
that  required  by  the  alum.  Any  deficiency  in  alkalinity  must  be 
corrected  by  adding  lime  or  soda  ash  to  the  raw  water,  0.35  grain 
of  lime  or  0.5  grain  of  soda  ash  being  required  per  grain  of  alum. 

These  relations  are  shown  by  Plate  IV  for  quick  and  slaked 
lime,  and  by  Plate  V  for  soda  ash,  used  in  conjunction  with 
aluminum  sulphate.  The  lower  margin  gives  the  amount  of  lime 
or  soda  ash  required  to  supplement  deficiencies  in  alkalinity.  The 
use  of  these  charts  in  connection  with  Plate  III  is  shown  by  the 
following  examples.  It  is  recommended  that  the  "  medium  " 
curve  on  Plate  III  be  used  with  a  new  water  and  to  serve  as  a  guide 
in  plotting  the  alum-turbidity  curve,  as  mentioned  above.  In  the 
interests  of  economy,  the  operator  should  endeavor  to  use  as  little 
coagulant  as  is  consistent  with  good  results. 

Example  1.     Analysis  of  raw  water: 

Turbidity,  800  parts  per  million 
Alkalinity,  50  parts  per  million 
Free  CO2,  0  part  per  million 

On  Plate  III,  left-hand  margin,  find  turbidity  800.  Follow  the 
horizontal  line  through  this  point  to  the  right  until  it  intersects 
the  "  medium  "  curve.  Follow  the  vertical  line  down  from  the 
intersection  and  read  2.5  grains  per  gallon  of  aluminum  sulphate 


148  WATER   PURIFICATION   PLANTS 

at  the  lower  margin.  To  find  the  equivalent  pounds  per  million 
gallons  follow  up  vertically  from  2.5  grains  to  the  intersection 
with  the  line  marked  "  Conversion  Line-Grains  per  Gallon  to 
Pounds  per  Million  Gallons,"  then  horizontally  to  the  right-hand 
margin,  where  read  357  pounds.  If  three  million  gallons  of  raw 
water  are  being  pumped  per  day,  the  amount  of  alum  required 
will  be  3X357,  or  1,871  pounds  per  day.  On  Plate  IV,  find  the 
intersection  of  the  2.5  grain  per  gallon  diagonal  with  the  left-hand 
margin  and  note  that  the  minimum  alkalinity  required  without 
lime  is  35.  Therefore,  an  alkalinity  of  50  is  ample  and  no  lime  is 
required.  Following  the  horizontal  line  from  alkalinity  35  to  its 
intersection  with  the  line  marked  "  Increase  in  C(V '  then  ver- 
tically to  the  upper  margin  shows  that  the  free  carbonic  acid  in 
the  settled  water  as  delivered  to  the  filters  will  be  increased  17 
parts  per  million.  The  C02  in  the  filtered  water  will  not  be  in- 
creased that  amount,  as  part  of  this  gas  will  be  liberated  and 
collect  in  the  filters,  due  to  the  pressure  in  the  sand  being  below 
atmospheric.  Following  from  the  intersection  of  the  2.5  grain 
diagonal  with  the  horizontal  line  marked  "  No  increase  in  CCV' 
vertically  upward  to  intersection  with  the  line  marked  "  Per- 
manent Hardness,"  then  horizontally  to  the  right-hand  margin, 
read  "  Increase  in  Permanent  Hardness  as  CaSCV  26.25  parts 
per  million. 

Example  2.     Analysis  of  raw  water: 

Turbidity,  250  parts  per  million 
Alkalinity,  20  parts  per  million 
Free  CO2,  5  parts  per  million 

On  Plate  III  for  turbidity  250,  find  alum  required,  1.85  grains  per 
gallon,  or  264  pounds  per  million  gallons.  On  Plate  IV,  estimating 
the  point  between  the  1.5  grain  per  gallon  and  the  2  grain  per  gal- 
lon diagonal  at  which  1.85  would  come,  follow  this  imaginary  diag- 
onal to  the  right  until  it  intersects  the  horizontal  line  through  20 
alkalinity.  From  this  intersection  follow  vertically  downward 
until  the  horizontal  line  through  "  O  "  is  reached,  and  then  follow 
the  diagonal  lines  downward  and  toward  the  right  until  the  hori- 
zontal line  through  5  on  the  "  H2SO4  Acidity  and  Free  CO2"  scale  is 
reached.  From  this  point  follow  vertically  downward,  and  read  lime 
required  as  0.55  grain  per  gallon.  To  get  the  result  in  pounds  per 
million  gallons,  follow  vertically  upward  from  0.55  to  the  con- 


COAGULATION   AND    STERILIZATION  149 

version  line,  then  to  the  right-hand  margin,  reading  79  pounds  per 
million  gallons.  In  this  case  the  increase  in  CO2  due  to  the  alum 
reaction  is  6.8  parts  per  million,  obtained  by  following  the  20 
alkalinity  line  to  the  right  until  it  intersects  the  "  Increase  in  CO2" 
line,  then  upward  to  the  upper  margin.  The  increase  in  permanent 
hardness  in  this  case  is  19.5  parts  per  million. 
Example  3.  Analysis  of  raw  water: 

Turbidity,  500  parts  per  million 
Alkalinity,  63  parts  per  million 
Free  C02,  8  parts  per  million 

Required  that  the  treated  water  shall  contain  no  Free  C02.  On 
Plate  III,  for  turbidity  500,  find  alum  required  2.0  grains  per 
gallon,  or  286  pounds  per  million  gallons,  using  the  "  medium  " 
curve.  On  Plate  IV,  follow  the  2.0  grain  per  gallon  diagonal  down 
to  the  horizontal  line  marked  "  Line  for  No  Increase  in  C02." 
Then  continue  along  the  2-grain-per-gallon  line  downward  and  dia- 
gonally to  the  right  until  it  intersects  the  horizontal  line  through 
8  on  the  "  H2SO4  Acidity  and  Free  C02"  scale.  Then  vertically 
downward  to  1.1  grains  per  gallon  on  the  lime  scale,  which  is 
equivalent  to  157  pounds  per  million  gallons.  This  will  give  a 
water  free  from  the  corrosive  action  of  carbonic  acid.  The  in- 
crease in  permanent  hardness  will  not  be  affected,  being  21  parts 
per  million  in  this  case. 

Example  4.  In  mining  regions  the  water  is  rendered  acid  by 
the  sulphuric  acid,  iron  and  aluminum  sulphate  from  the  mine 
waste.  Such  a  water  gives  a  negative  test  for  alkalinity  as  evi- 
denced by  the  sample  remaining  white  when  erythrosin  is  added, 
and  is  therefore  titrated  with  sodium  carbonate,  the  results  being 
recorded  as  "  H2SO4  Acidity."  Such  a  water  may  analyze  as 
follows : 

Turbidity,  3  parts  per  million 

Alkalinity,  0  part  per  million 

H2S04  acidity,  12  parts  per  million 
Free  C02,  3  parts  per  million 

On  Plate  III,  for  turbidity  3,  find  alum  required  0.3  grain  per 
gallon,  or  43  pounds  per  million  gallons.  On  Plate  IV,  following  a 
proportional  distance  below  the  0.5  grain  per  gallon  line  (the 
lowest  one),  find  the  intersection  with  the  horizontal  line  through 


150  WATER   PURIFICATION    PLANTS 

15  on  the  "  H2S04  Acidity  and  Free  COz"  scale,  thence  vertically 
downward  to  lime  required  0.86  grain  per  gallon,  or  123  pounds 
per  million  gallons.  Note  that  the  acidity  and  CO2  are  added 
(12+3=15),  and  considered  together.  If  analyses  show  a  con- 
siderable amount  of  iron  present  in  addition  to  the  sulphuric  acid, 
a  reduction  in  the  amount  of  alum  may  be  made,  as  will  be  ex- 
plained later. 

Aluminum  sulphate  is  very  soluble  in  water  and  solutions  are 
easily  prepared.  The  required  amount  is  weighed  out  and  placed 
in  a  perforated  box  over  the  solution  tank,  see  Fig.  8,  and  hot 
water  is  sprayed  over  it,  which  dissolves  the  alum  and  washes  it 
into  the  solution  tank.  Enough  water  is  added  to  make  up  a 
solution  of  proper  strength,  which  is  thoroughly  mixed  by  means 
of  the  revolving  paddles  in  the  solution  tank.  It  is  not  necessary 
to  operate  the  paddles  after  the  solution  is  made  up.  For  amounts 
of  water  required  see  Plate  XI  and  page  168;  see  also  the  chapter 
on  general  operation.  The  strength  of  solution  used  is  generally 
between  3  and  6  per  cent.  Alum  may  also  be  fed  dry  by  means  of 
automatic  scales,  such  as  were  described  for  lime  in  connection 
with  the  Columbus  plant.  Under  such  conditions  it  is  generally 
necessary  to  crush  it  quite  fine,  generally  to  half -inch  lumps  or  finer. 

Lime.  Quicklime  or  calcium  oxid  (CaO)  is  used  with  alu- 
minum and  ferrous  sulphate  in  coagulation,  furnishing  the  hydrox- 
yl  ions  (OH'),  necessary  to  the  formation  of  ajuminum  and  iron 
hydroxid  (A12(OH)6,  and  Fe(OH)2).  It  is  also  used  in  water- 
softening.  In  appearance  it  is  a  white,  chalky  substance,  usually 
in  both  lumps  and  powder.  For  convenience  in  handling  it  should 
be  specified  to  be  crushed,  so  that  no  lumps  exceed  2  inches  in 
largest  dimension.  If  it  is  to  be  weighed  out  automatically,  it 
should  preferably  be  crushed  to  %  inch  or  smaller.  Lime  con- 
tains a  variable  amount  of  impurities,  depending  on  the  region 
from  which  the  limestone  from  which  it  is  prepared  is  obtained, 
and  the  care  used  in  burning.  Some  limes  contain  only  50  per 
cent  of  water-soluble  calcium  oxid,  but  those  used  for  coagulative 
purposes  generally  run  from  75  to  99  per  cent.  Unless  the  source 
of  supply  is  too  remote,  a  high  calcium  lime  should  be  obtained,  as 
it  is  more  satisfactory  to  use,  slaking  more  rapidly,  reacting  more 
readily  in  solution,  etc.  A  higher  price  (delivered  at  the  plant) 
is  justified  for  a  high  calcium  lime  over  that  for  a  leaner  one. 
Thus  if  lime  from  one  kiln  analyzing  80  per  cent  CaO  costs  24 


COAGULATION   AND    STERILIZATION  151 

cents  per  100  pounds,  and  that  from  another  analyzes  90  per  cent 
CaO,  the  latter  is  to  be  preferred  at  any  price  up  to  9/8  of  24,  or 
27  cents. 

Lime  can  be  obtained  in  bags,  barrels,  or  in  bulk,  by  carload 
lots.  It  should  be  fresh-burned  when  bought,  as  it  deteriorates 
with  storage.  For  this  reason,  if  bought  in  barrels  or  bags,  large 
quantities  should  not  be  kept  on  hand,  as  the  carbonic  acid  in  the 
air  will  partially  change  it  into  calcium  carbonate.  In  a  moist 
atmosphere  it  will  slake,  expanding  in  volume  in  so  doing,  and 
bursting  the  containing  package.  In  the  larger  plants  it  is  stored 
in  air-tight  concrete  bins,  which  is  undoubtedly  the  best  method. 

If  possible  it  should  be  bought  on  a  guaranteed  percentage  of 
calcium  oxid,  a  sample  of  each  shipment  being  analyzed  (see 
Appendix  A) .  If  the  analysis  falls  below  the  guarantee  a  deduction 
should  be  made;  if  it  is  above  the  guaranteed  amount,  a  bonus 
should  be  paid. 

Quicklime  must  be  slaked  before  use,  by  adding  water  to  it, 
thereby  converting  it  into  calcium  hydroxid,  the  reaction  being: 

CaO+H2O  =  Ca(OH)2 

The  slaking  should  be  very  carefully  done,  as  on  it  depends  the 
success  of  the  lime  treatment.  In  large  plants  it  is  usually  ac- 
complished in  iron  tanks,  the  lime  and  water  being*  mixed  with 
motor-driven  rakes.  In  small  plants  an  iron  trough  or  slaking  box 
is  used.  It  is  well  to  use  a  minimum  amount  of  water  and  to  cover 
the  lime  while  slaking,  allowing  it  to  heat  up  during  the  process. 
Also  the  lime  and  water  must  be  mixed  so  that  every  part  thereof 
comes  in  intimate  contact  with  the  water.  Theoretically  it  takes 
J^  as  much  water  as  lime,  but  practically  about  4  times  as  much 
water  by  weight  as  lime  is  required.  The  water  used  should  be 
as  hot  as  possible,  so  that  the  temperature  during  slaking  may  be 
high,  if  possible  200°  Fahr.  A  95  per  cent  lime  requires  about  15 
to  30  minutes  to  slake  thoroughly  under  optimum  conditions,  and 
the  leaner  a  lime  is  the  longer  it  requires.  If  possible,  the  lime 
for  each  shift  should  be  slaked  in  the  shift  before. 

The  slaked  lime  is  diluted  with  water  and  kept  in  solution 
tanks,  from  which  it  is  fed  to  the  raw  water  through  an  orifice  box. 
At  least  four  times  as  much  water  by  weight  as  slaked  lime  is  re- 
quired to  make  a  satisfactory  dilution,  and  the  water  used  in  this 
case  should  be  as  cold  as  possible,  as  calcium  hydroxid  is  more 
soluble  in  cold  water. 


152  WATER   PURIFICATION   PLANTS 

Stirring  paddles  in  the  solution  tanks  must  be  kept  going  con- 
stantly, in  order  to  keep  the  lime  in  suspension.  Owing  to  its 
clogging  nature,  the  orifice  boxes  and  piping  through  which  it 
flows  must  be  carefully  watched  and  frequently  cleaned  to  prevent 
choking.  If  the  lime  solution  is  introduced  into  the  raw  water  by 
means  of  a  single  pipe,  entering  as  a  solid  stream,  much  of  it  will 
fall  to  the  bottom  and  be  lost.  It  is  best  introduced  through  a  pipe 
or  grid  with  comparatively  large  perforation,  say,  %  or  Y^  inch, 
using  a  solution  as  dilute  as  possible. 

Unless  the  above  precautions  as  to  proper  storage,  slaking,  and 
introduction  are  observed,  a  large  loss  will  result,  which  may  be  as 
much  as  50  per  cent.  By  proper  handling  this  loss  may  be  re- 
duced to  10  or  15  per  cent. 

The  use  of  an  excess  of  lime  should  be  avoided,  as  it  renders  the 
water  caustic.  This  is  best  done  by  keeping  the  dose  of  lime 
within  the  limits  dictated  by  the  tests  for  free  and  half-bound 
carbonic  acid,  and  the  amount  required  to  react  with  the  coagulant 
used,  as  indicated  by  the  Plates.  The  treated  water  can  also  be 
tested  for  alkalinity  with  both  phenolphthalein  and  erythrosin. 
The  alkalinity  with  the  former  indicator  should  not  exceed  half 
of  that  with  the  latter.  This  does  not  necessarily  mean  that  there 
is  no  caustic  alkalinity  present,  but  indicates  that  lime  is  present 
in  correct  quantity  to  react  with  all  the  bicarbonates,  given  suf- 
ficient time  for  the  completion  of  the  reaction.  Another  test 
for  calcium  hydroxid  consists  in  adding  a  few  drops  of  dilute  silver 
nitrate  solution  to  a  sample  of  water  in  a  test  tube.  A  grayish 
brown  precipitate  indicates  the  presence  of  calcium  hydroxid 
(caustic  alkalinity).  This  test  is  not  reliable  with  waters  con- 
taining chlorids  in  appreciable  quantities. 

Hydrated  Lime.  Hydrated  lime  (Ca(OH)2)  may  be  obtained 
in  paper  bags  of  40  pounds  each,  or  in  duck  bags  of  100  pounds 
(a  rebate  is  allowed  on  the  bags) .  It  has  several  advantages  over 
quicklime.  It  need  not  be  slaked,  and  the  losses  and  danger  from 
improper  slaking  are  thus  avoided.  It  does  not  deteriorate  in 
storage.  It  is  purer  than  most  quicklimes.  The  accrued  savings 
from  these  several  sources  compensate  for  its  greater  weight,  so 
that  it  may  be  substituted  in  Plate  IV  without  change.  It  may  be 
mixed  directly  in  coagulant  tanks  and  fed  to  the  orifice  boxes  as  an 
emulsion,  in  which  case  the  same  precautions  against  clogging 
as  for  quicklime  must  be  observed.  Or  it  may  be  fed  in  powdered 


COAGULATION   AND    STERILIZATION 


153 


form  into  a  stream  of  running  water  by  means  of  a  screw  feed,  the 
stream,  after  receiving  the  lime,  falling  into  a  funnel  and  flowing 
through  a  pipe  into  the  raw-water  main.  The  screw  feed  is  driven 


Friction  Drive 


Screw  Feed 


Pipe  to  Raw  Water 


FIG.  74. — Dry  Chemical  Feeding  Device. 

by  a  water  motor  through  a  friction,  drive  which  allows  for  reg- 
ulating the  speed  of  the  screw.  Suitable  reduction  gearing  is 
provided  for  lowering  the  speed  of  the  motor  to  that  required  for 
the  screw.  The  freedom  from  clogging  and  positiveness  of  feed 
with  this  method  are  obvious.  To  prevent  the  lime  in  the  hopper 


154  WATER    PURIFICATION    PLANTS 

from  arching,  a  scraper  attached  to  the  screw  shaft  is  added. 
(Fig.  74.)* 

Hydrated  lime  costs  more  than  quicklime,  owing  to  its  in- 
creased weight  (caused  by  the  water  of  hydration),  which  is  32 
per  cent  greater  than  quicklime  for  the  same  amount  of  calcium 
oxid. 

Soda  Ash.  This  is  anhydrous  sodium  carbonate  (Na2C03). 
It  is  a  fine  white  powder  and  is  generally  obtainable  in  duck  bags 
of  100  pounds  each  (a  rebate  is  allowed  on  the  bags).  It  should  be 
specified  to  contain  98  per  cent  pure  sodium  carbonate,  and  not 
over  0.5  per  cent  insoluble  matter. 

It  is  used  with  alum  in  the  same  manner  as  lime  and  in  the 
proportions  shown  graphically  by  Plate  V.  It  may  also  be  used 
for  the  removal  of  free  CO2,  and  for  acid  correction.  It  has  the 
advantage  of  not  increasing  the  permanent  hardness  of  the  water, 
and  is  much  easier  to  handle  than  lime,  dissolving  readily,  not 
requiring  stirring  in  the  coagulant  tanks,  and  not  clogging  orifice 
boxes  or  piping.  By  its  use  after-precipitation  of  calcium  car- 
bonate on  the  filter  sand  and  in  the  mains  is  avoided — an  impor- 
tant point.  Used  with  alum  in  the  proportions  required  for  the 
theoretic  reaction,  0.5  grain  per  gallon  per  grain  of  aluminum  sul- 
phate, a  small  amount  of  free  carbonic  acid  is  produced,  half  as 
much  as  when  the  alum  reacts  with  the  natural  alkalinity.  By 
using  equal  amounts  of  soda  ash  and  alum  no  free  carbonic  acid  is 
formed.  Soda  ash  is  very  much  used  in  small  plants,  owing  to  the 
convenience  in  handling  and  because  not  such  great  care  is  re- 
quired to  use  the  exact  proportions  as  with  lime,  also  where  the 
settling  capacity  is  limited,  say,  less  than  4  to  6  hours,  lime  would 
cause  trouble  by  after-precipitation,  while  soda  ash  does  not.  Its 
principal  disadvantage  is  its  cost,  as  more  is  required  than  of  lime, 
and  its  price  is  about  three  times  as  great.  (See  paragraph  on 
comparative  costs.) 

The  following  examples  will  explain  the  use  of  Plate  V  in  de- 
termining the  amount  of  soda  ash  to  use: 

Example  1.  Analysis  of  raw  water: 

Turbidity,  800  parts  per  million 
Alkalinity,  50  parts  per  million 
Free  CO2,  0  part  per  million 


South  Pittsburgh  Water  Co. 


COAGULATION   AND    STERILIZATION  155 

As  before,  the  amount  of  alum,  as  determined  from  Plate  III,  is 
2.5  grains  per  gallon.  Referring  to  Plate  V,  it  will  be  seen  that 
for  2.5  grains  an  alkalinity  of  35  is  required,  so  that  no  soda  ash 
is  needed.  Referring  to  the  line  "  Increase  in  CO2  Using  Natural 
Alkalinity,"  this  will  be  found  to  be  17  parts  per  million,  as  in 
Example  1,  under  lime.  The  permanent  hardness  is  not  given, 
but  can  be  found  from  Plate  IV.  For  2.5  grains  this  is  26.25  parts 
per  million. 

Example  2.  Analysis  of  raw  water: 

Turbidity,  250  parts  per  million 
Alkalinity,  20  parts  per  million 
Free  CO2,  5  parts  per  million 

On  Plate  III,  for  turbidity  250,  find  alum  required  1.85  grains  per 
gallon.  On  Plate  V,  estimating  the  point  between  the  1.5  grains 
per  gallon  and  the  2  grains  per  gallon  diagonal  at  which  1.85 
would  come,  follow  this  imaginary  diagonal  to  the  right  until  it 
intersects  the  horizontal  line  through  20  alkalinity.  From  this 
intersection  follow  down  vertically  to  the  0  horizontal,  then  diag- 
onally to  the  right,  paralleling  the  dashed  lines  marked  "  Lines 
for  Removal  of  CQz"  until  the  horizontal  line  through  5  on  the 
"  H2SO4  Acidity  and  Free  CW  scale  is  reached.  Following  ver- 
tically downward  from  this  point,  read  1.2  grains  per  gallon  on  the 
soda-ash  scale,  which  by  the  conversion  line  is  found  to  be  172 
pounds  per  million  gallons.  The  increase  in  C02  due  to  the  re- 
action of  the  alum  and  natural  alkalinity  is  6.8  parts  per  million, 
obtained  by  following  the  20  alkalinity  line  to  the  right  until  it 
intersects  the  line  marked  "  Increase  in  CO2  Using  Natural 
Alkalinity,"  then  upward  to  the  upper  margin.  Such  a  treat- 
ment would  be  used  where  it  is  desired  not  to  remove  all  the  CO2, 
but  to  keep  this  below  a  certain  amount,  say  10  parts  per  million. 
This  is  sometimes  done  for  economic  reasons,  and  is  not  very 
objectionable  if  the  water  is  fairly  high  in  alkalinity. 
Example  3.  Analysis  of  raw  water: 

Turbidity,  500  parts  per  million 
Alkalinity,  63  parts  per  million 
Free  CO2,  8  parts  per  million 

Required  that  the  treated  water  shall  contain  no  CO2.  On  Plate 
III,  for  turbidity  500,  find  alum  required  2  grains  per  gallon.  On 


156  WATER    PURIFICATION    PLANTS 

Plate  V,  follow  the  dashed  line  for  2  grains  per  gallon  diagonally 
to  the  right,  then  downward  and  again  to  the  right,  until  it  inter- 
sects the  horizontal  line  through  8  on  the  "  H2SO4  Acidity  and 
Free  CO2"  scale.  Then  vertically  downward  to  the  soda-ash  scale, 
reading  3.2  grains  per  gallon,  which  by  the  conversion  scale  is 
found  to  be  458  pounds  per  million  gallons. 
Example  4.  Analysis  of  raw  water : 

Turbidity,  3  parts  per  million 

Alkalinity,  0  part  per  million 

H2SC>4  acidity,      12  parts  per  million 

On  Plate  III,  for  turbidity  3,  find  alum  required  0.3  grain  per 
gallon.  On  Plate  V,  following  a  proportional  distance  below  the 
0.5  grain  per  gallon  line  (the  lowest  one)  diagonally  to  the  right, 
then  vertically  downward  and  again  to  the  right,  paralleling  the 
solid  diagonal  lines  marked  "  Lines  for  Removal  of  H2SO4,"  until 
the  horizontal  through  12  on  the  "  H2S04  Acidity  and  Free  CO2" 
scale  is  intersected.  Thence  vertically  downward,  reading  0.93 
grain  per  gallon  on  the  soda  scale.  There  would  be  a  formation 
of  CO2  using  this  amount  of  soda  ash.  If  a  C02-free  water  is 
desired  use  the  dashed  lines  both  for  the  alum  and  the  acid,  as  in 
Example  III.  If  both  CO2  and  sulphuric  acid  occur,  add  them 
together,  and  use  the  dashed  lines  to  secure  a  complete  removal. 

Soda  ash  may  be  dissolve'd  and  fed  to  the  water  in  the  same 
manner  as  aluminum  sulphate,  using  a  dissolving  box  and  solution 
tank  arranged  as  in  Fig.  8.  The  solution  should  not  exceed  5  per 
cent  in  strength.  Stirring  is  necessary  only  while  making  up  the 
solution.  It  may  also  be  fed  to  the  water  by  means  of  the  device 
described  for  use  with  hydrated  lime,  as  well  as  with  automatic 
scales  of  the  type  used  at  the  Columbus  plant. 

Ferrous  Sulphate.  Ferrous  sulphate,  in  conjunction  with  lime, 
is  extensively  used  as  a  coagulant.  The  commercial  product  con- 
sists of  transparent  green  lumps,  composed  of  the  crystals  of  the 
salt.  It  is  quite  pure,  running  from  95  per  cent  ferrous  sulphate 
upward.  Its  chemical  formula  is  FeSO4,7H2O,  containing  seven 
molecules  of  water.  On  prolonged  exposure  to  the  air,  the  sur- 
face is  slightly  oxidized,  forming  ferric  sulphate  and  iron  oxid. 

A  second  form,  known  as  "  sugar  of  iron,"  is  also  used.  This  is 
partially  dehydrated,  containing  less  than  seven  molecules  of  water 
of  crystallization,  so  that  it  contains  over  100  per  cent  of  ferrous 


COAGULATION   AND   STERILIZATION 


157 


sulphate  (FeSO4,7H20).  It  is  quite  pure,  containing  less  than  1 
per  cent  of  foreign  matter.  In  appearance  it  is  granular,  like  sugarr 
making  it  very  convenient  for  use  in  dry  feeding  as  described  under 
hydrated  lime  (see  Fig.  74),  the  same  type  of  apparatus  being  used. 
Its  advantages  are  that  the  cost  of  treatment  is  generally 
cheaper  than  with  alum,  especially  with  very  turbid  waters,  and 


FIG.  75. — Iron  Sulphate  and  Coagulation. 

that  the  coagulum  or  "  flock  "  formed  is  of  greater  specific  gravity 
than  in  the  case  of  alum,  causing  a  more  rapid  sedimentation. 
Also,  the  ferrous  and  ferric  sulphate  seem  to  have  a  direct  germicidal 
action  to  a  certain  extent.  On  the  other  hand,  the  use  of  lime  is  re- 
quired at  all  times,  with  its  concomitant  danger  of  trouble  from 
after-precipitation,  if  it  is  not  carefully  gaged,  due  to  the  re- 
action of  the  surplus  with  the  bicarbonate  alkalinity,  the  resulting 
product,  calcium  carbonate,  being  slow  to  form  and  settle  out. 
It  cannot  well  be  used  with  colored  swamp  water,  as  the  ferrous 
sulphate  forms  complex  soluble  compounds  with  the  organic 
matter  present,  which  often  give  the  water  a  blackish  tinge.  It  is 
difficult  to  use  with  soft  waters,  as  any  surplus  lime  would  make  the 
water  caustic,  also  soft  waters  are  very  apt  to  be  highly  colored. 
For  these  reasons  this  process  has  found  its  most  extensive  and  sue- 


158  WATER    PURIFICATION    PLANTS 

cessful  application  to  turbid  waters  of  fairly  high  alkalinity,  such 
as  those  of  the  Mississippi  and  Missouri  River  valleys. 

The  reactions  may  be  considered  in  two  ways:  if  the  lime  is 
added  before  the  ferrous  sulphate  the  two  react  directly: 

FeSO4+Ca(OH)2  =  Fe(OH)2+CaSO4 

If  the  ferrous  sulphate  is  added  first,  the  reactions  are  more 
complex.  The  sulphate  reacts  with  the  bicarbonates  in  the  water, 
forming  a  bicarbonate  of  iron,  which  stays  in  solution: 

FeS04+CaC03H2C03  =  FeCO3H2CO3+CaS04 

This  would  oxidize  and  precipitate,  but  the  reaction  is  slow  and 
the  precipitate  often  forms  in  a  finely  divided  state,  so  that  lime 
is  added  to  complete  the  reaction: 

FeC03H2C03+Ca(OH)2  =  Fe(OH)2+CaC03H2C03 

The  effective  coagulum  is  the  ferrous  hydroxid  Fe(OH)2,  a  gelat- 
inous precipitate.     In  its  pure  form  this  is  white,  slightly  soluble, 
giving  the  water  a  ferruginous  taste.     It  is  rapidly  oxidized  by  the 
dissolved  oxygen  in  the  water,  according  to  the  reaction, 
4Fe(OH)2+2H2O+O2  =  2Fe2(OH)6 

The  ferric  hydroxid  formed  (Fe2(OH)6)  is  an  insoluble  gelatinous 
precipitate  of  a  brown  color.  In  practice  intermediate  (ferro- 
ferric)  hydroxids  of  a  green  color  are  often  formed,  particularly  if 
some  of  the  ferrous  sulphate  is  oxidized  to  ferric  before  the  lime 
reacts  with  it.  After  precipitating,  the  ferro-ferric  and  ferric 
hydroxids  may  be  converted  into  iron  oxids,  by  the  splitting  off 
of  the  water  of  hydration: 


these  oxids  forming  a  heavy  silt  varying  in  color  from  yellow  to 
brown,  or  almost  black  (due  to  the  presence  of  dehydrated  ferro- 
ferric  hydroxid)  .  The  amount  of  dissolved  oxygen  required  in  the 
water  for  these  reactions  is  not  large,  0.5  part  per  million  being 
required  for  each  grain  per  gallon  of  ferrous  sulphate.  A  normal 
stream  should  contain  at  least  5  parts  per  million  of  dissolved 
oxygen,  even  in  midsummer,  so  that  it  would  take  care  of  10  grains 
per  gallon  of  iron.  A  badly  polluted  stream  might  contain  only 
2  parts  of  oxygen  during  the  same  season,  causing  some  trouble, 
due  to  the  solubility  and  taste  of  the  unoxidized  ferrous  hydroxid. 
Theoretically,  the  amount  of  lime  required  is  0.24  grain  of  85 


COAGULATION   AND    STERILIZATION  159 

per  cent  CaO  for  each  grain  of  ferrous  sulphate.  Practically  the 
minimum  used  is  about  0.4  grain  per  grain  of  iron  (see  sources  of 
loss  under  "  Lime  "),  and  it  is  sometimes  an  advantage  to  in- 
crease the  lime,  if  sufficient  alkalinity  is  present,  as  the  resulting 
calcium  carbonate  crystallizes  about  the  ferric  hydroxid  and  in- 
creases its  weight  and  rapidity  of  settling.  The  amount  of  calcium 
sulphate  formed  is  8.44  parts  per  million  for  each  grain  per  gallon 
ferrous  sulphate. 

In  addition  to  the  coagulative  effect,  we  have  somewhat  of  the 
"  adsorptive  "  action  toward  dissolved  matters,  found  in  the  case 
of  aluminum  sulphate,  and,  in  addition,  ferric  sulphate  will  pre- 
cipitate nitrogenous  organic  matters  in  solution  as  non-putre- 
factive compounds. 

In  practical  operation,  at  least  enough  lime  must  be  added  to: 
1st,  combine  with  the  iron  sulphate;  2d,  \,o  remove  any  CO2  that 
may  be  present;  3d,  to  give  a  slight  excess,  1  to  5  parts  per  million. 
The  treated  water  should  be  faintly  pink  with  phenolphthalein. 
The  amount  of  lime  used  is  generally  increased  with  the  turbidity. 
Commencing  with  0.4  grain  for  a  practically  clear  water,  the  in- 
crease would  be  such  that  the  amounts  of  lime  and  ferrous  sulphate 
would  be  equal  for  a  turbidity  of  about  1,200,  the  lime  increasing 
still  farther  for  higher  turbidities.  These  relations  are  diagrammed 
on  Plate  VI,  which  shows  the  relations  between  the  turbidity  of 
the  water  and  the  amounts  of  ferrous  sulphate  and  lime,  also  giving 
a  curve  for  converting  grains  per  gallon  of  lime  or  sulphate  to 
pounds  per  million  gallons,  and  another  curve  for  converting 
Hazen  Reciprocal  Turbidity  to  the  United  States  Geological 
Survey  Standard,  which  will  be  found  convenient  in  the  older 
plants,  where  the  former  standard  may  be  in  use.  Of  course  the 
amount  of  lime  used  must  be  governed  by  the  bicarbonate  al- 
kalinity of  the  raw  water,  no  more  being  used  than  can  combine 
with  the  bicarbonates  and  the  ferrous  sulphate. 

The  proper  amounts  of  lime  and  iron  under  any  given  condi- 
tions can  be  most  readily  determined  from  Plates  VI  and  VII,  as 
illustrated  in  the  following  examples: 

Example  1.  Analysis  of  raw  water: 

Turbidity,  400  parts  per  million 
Bicarbonates,  60  parts  per  million 
Free  CO2,  10  parts  per  million 


160  WATER    PURIFICATION    PLANTS 

On  Plate  VI,  tracing  to  the  right  along  the  horizontal  through  400 
turbidity  until  the  "  Turbidity-Ferrous  Sulphate  Curve "  is 
reached,  then  vertically  downward,  read  1.83  on  the  lower  scale, 
"  Ferrous  Sulphate  (FeSO47H2O)  in  Grains  per  Gallon."  In  a 
similar  manner  determine  the  corresponding  amount  of  lime  as 
1.15  grains  per  gallon  (on  the  lower  scale).  By  means  of  the 
"  Conversion  Line — Grains  per  Gallon  to  Pounds  per  Million 
Gallons,"  these  are  found  to  be  equal  to  262  and  165  pounds  per 
million  gallons  for  ferrous  sulphate  and  lime  (85  per  cent  CaO  or 
95  per  cent  hydrate),  respectively,  reading  the  values  from  the 
scale  on  the  right  margin.  Note  that  both  of  these  values  are 
approximate,  varying  with  different  waters,  and  that  the  operator, 
when  once  familiar  with  the  water  he  is  treating,  should  vary  from 
these  curves  according  to  the  dictates  of  his  experience. 

Referring  to  Plate  VII,  tracing  horizontally  to  the  right  from 
1.83  grains  per  gallon  on  the  Iron  Sulphate  scale,  and  vertically 
upward  from  1.15  grains  per  gallon  on  the  Lime  scale,  follow  from 
the  intersection  of  these  lines  downward  parallel  to  the  diagonals 
until  the  "  Lime- Alkalinity  Relation "  line  is  reached,  then 
horizontally  to  the  "  Bicarbonate  Alkalinity  "  scale  on  the  right, 
where  read  15  parts  per  million  as  the  required  amount  for  this 
relation  of  iron  and  lime.  Therefore  the  bicarbonates  in  the  water 
(60  p. p.m.)  are  ample  to  react  with  the  surplus  of  lime  being  used. 
To  find  the  total  lime  required,  including  that  for  CO2  removal, 
trace  upward  from  1.15  on  the  Lime  scale  to  the  0  horizontal,  then 
follow  the  diagonals  downward  and  to  the  right  until  the  horizon- 
tal through  10  on  the  "  H2SO4  Acidity  and  Free  C02  "  scale  is 
reached,  then  vertically  downward,  reading  1.65  on  the  Lime  scale. 
By  means  of  the  conversion  line  this  is  found  to  equal  236  pounds 
per  million  gallons.  The  increase  in  permanent  hardness  is  found 
by  tracing  horizontally  to  the  right  from  1.83  on  the  "  Iron 
Sulphate  "  scale  until  the  line  marked  "  Increase  in  Permanent 
Hardness  "  is  reached,  then  vertically  upward  to  the  "Permanent 
Hardness  "  scale,  where  read  15.4  parts  per  million. 

Example  2.  Analysis  of  raw  water: 

Turbidity,  2,000  parts  per  million 
Bicarbonates,  57  parts  per  million 
Free  CO2,  12  parts  per  million 

From  Plate  VI,  for  a  turbidity  of  2,000,  find  the  amount  of  ferrous 


COAGULATION   AND    STERILIZATION  161 

sulphate  required  to  be  4  grains  per  gallon.  It  is  evident  that  the 
low  bicarbonate  alkalinity  may  limit  the  amount  of  lime  which 
can  be  used.  To  determine  the  maximum  amount  of  lime  allow- 
able, refer  to  Plate  VII.  Find  57  on  the  "  Bicarbonate  Alkalinity  " 
scale  and  trace  horizontally  to  the  left  until  the  "  Lime-Alkalinity  " 
curve  is  reached,  then  proceed  upward  along  the  diagonal  until  on 
the  horizontal  through  4  grains  per  gallon  on  the  "  Iron  Sulphate  " 
scale.  From  this  point  drop  vertically  to  the  0  horizontal  and 
follow  the  diagonal  for  C02  correction.  When  on  the  horizontal 
through  12  on  the  "  H2SO4  Acidity  and  Free  CO2"  scale,  drop  ver- 
tically to  the  Lime  scale,  where  read  4.05  grains  per  gallon  of  lime, 
or  by  the  conversion  line,  580  pounds  per  million  gallons.  The 
increase  in  permanent  hardness  for  4  grains  per  gallon  of  iron  sul- 
phate is  found,  from  Plate  VII,  to  be  33.7  parts  per  million. 

In  the  case  of  a  water  containing  no  alkalinity  and  both  H2S04 
acidity  and  free  CO2,  use  the  minimum  amount  of  lime  to  com- 
bine with  the  ferrous  sulphate,  and,  adding  the  H2SO4  and  CO2 
together,  determine  from  the  CO2  diagonals  the  additional  amount 
of  lime  required  to  counteract  these  acidities. 

As  already  said,  an  excess  of  lime  should  be  carefully  avoided, 
as  most  of  the  troubles  experienced  with  the  iron  and  lime  treat- 
ment result  from  this  cause. 

In  most  waters  it  is  found  best  to  introduce  the  lime  first,  as 
if  the  iron  is  added  first,  the  bicarbonate  of  iron  formed  is  not  so 
readily  acted  upon  by  the  lime,  or,  at  most,  is  reduced  to  a  car- 
bonate, which  is  apt  to  give  a  fine  powdery  sediment,  very  difficult 
to  settle  out. 

An  excess  of  iron  is  most  likely  to  result  with  acid  water,  and  is 
indicated  by  the  logwood  test  on  the  settled  water  and  by  the  fact 
that  the  settled  water  is  acid  with  erythrosin.  The  obvious 
remedy  is  more  lime. 

A  thorough  mixing  of  the  chemicals  is  most  essential  to  the 
success  of  this  process,  but  it  must  not  be  too  violent,  as  the 
coagulum  is  very  delicate.  For  the  same  reason  the  flow  through 
the  settling  basin  should  be  unbroken,  and  the  rate  of  "filtration 
lowered  to  100  million  gallons  per  acre  per  day. 

Solutions  of  crystalline  ferrous  sulphate  are  made  in  a  manner 
precisely  similar  to  that  used  for  aluminum  sulphate  and  with  the 
same  arrangement  of  dissolving  box  and  solution  tank.  Difficulty 
is  sometimes  experienced  due  to  the  oxidation  of  the  solution  to  the 


162  WATER   PURIFICATION   PLANTS 

ferric  condition.  This  can  be  avoided  to  a  large  extent  by  pro- 
viding covers  for  the  tanks  and  reducing  the  stirring  to  a  minimum. 
Crystalline  ferrous  sulphate  cannot  be  fed  in  the  dry  form,  as  to  do 
so  would  require  that  it  be  crushed  to  a  small  size.  On  being 
crushed  it  becomes  moist  and  cakes  badly. 

Sugar  of  iron  may  also  be  fed  as  a  solution,  but  is  particularly 
adapted  for  use  where  a  dry  feed  is  desirable.  It  may  be  fed  by 
means  of  the  device  shown  for  hydrated  lime,  Fig.  74,  or  by  mea- 
surement through  an  orifice,  since  it  will  flow  quite  freely  in  the  dry 
state.  Solutions  of  iron  sulphate  should  not  be  stronger  than  6 
per  cent. 

Natural  Coagulation.  Acid  mine  waters  sometimes  contain 
natural  sulphates  of  aluminum  and  iron,  the  latter  being  most 
frequent.  In  such  a  case  it  is  only  necessary  to  add  the  proper 
amount  of  lime  to  obtain  a  good  coagulation,  or,  if  not  sufficient, 
it  may  be  supplemented  with  ferrous  or  aluminum  sulphate.  If 
the  amounts  of  iron  and  acidity  (as  H2SO4)  have  been  determined, 
the  equivalent  coagulating  value  in  terms  of  ferrous  sulphate  may 
be  found  from  Plate  VIII,  and  the  amount  of  alum  or  iron  re- 
quired may  be  reduced  to  this  extent.  This  is  illustrated  by  the 
following  examples: 

Example  1. 

Iron  in  raw  water,  10  parts  per  million 

Acidity  of  raw  water,  25  parts  per  million 

Amount  alum  being  used,  4  grains  per  gallon 

Follow  the  horizontal  through  10  on  the  "  Iron  in  Parts  per 
Million  "  scale  to  the  right  until' the  heavy  diagonal  line  is  reached. 
Tracing  from  this  point  vertically  upward,  the  coagulating  value 
may  be  read,  and  tracing  downward  and  to  the  right,  paralleling 
the  diagonal  lines,  gives  the  required  acidity.  In  this  case  the 
coagulating  value  is  equivalent  to  2.85  grains  per  gallon  of  ferrous 
sulphate  and  the  required  acidity  is  17.5  parts  per  million,  which, 
being  less  than  the  acidity  of  the  raw  water,  is  satisfactory.  The 
amount  of  alum  which  must  be  added  to  give  a  coagulant  equiva- 
lent of  4grainsper  gallon  is4.00  minus  2.85  or  1.15  grains  per  gallon. 
Example  2.  Suppose  that  in  Example  1  the  acidity  had  been 
only  10  parts  per  million.  In  this  case  it  would  govern  the  coagulat- 
ing value.  The  procedure  would  then  consist  in  following  the 
diagonal  upward  from  10  on  the  "  Required  Acidity  "  scale  to  its 


COAGULATION   AND    STERILIZATION  163 

termination  in  the  heavy  line,  then  vertically  upward  to  the  upper 
margin,  where  the  coagulating  value  is  found  to  be  1.62  grains  per 
gallon. 

Introduction  of  Chemicals.  Very  commonly  the  chemicals 
used  in  coagulation  are  introduced  through  separate  pipes  into  the 
main  leading  from  the  raw-water  pumps  to  the  sedimentation 
basin,  and  while  this  is  moderately  satisfactory  under  ordinary 
conditions,  it  is  often  an  advantage  to  apply  the  chemicals  at  some 
other  point,  or  at  several  points.  If  the  raw  water  contains  a  large 
amount  of  heavy  sediment  or  clay,  as  during  a  flood,  it  would  be 
useless  to  introduce  any  chemicals  before  the  water  enters  the 
basin,  as  a  portion  of  these  would  be  absorbed  by  the  clay  and 
the  remainder  carried  down  with  the  clay  particles  soon  after 
entering.  In  such  a  case  it  is  advisable  to  let  the  heavy  sus- 
pended matter  settle  out  in  the  first  half  of  the  basin  without 
coagulation,  and  apply  the  chemicals  near  the  center  of  the  basin, 
using  a  perforated  pipe  extending  across  the  basin.  If  the  raw 
water  is  very  clear,  so  that  no  coagulation  is  required  to  assist  in 
removing  the  "  turbidity  "  (the  suspended  matter  being  generally 
gaged  and  known  by  this  characteristic),  and  no  organic  matter  is 
present,  the  chemicals  necessary  to  form  the  gelatinous  "  mat  " 
on  the  filters  are  best  added  as  the  water  is  leaving  the  sedimenta- 
tion basin.  For  river  waters  and  others  subject  to  large  fluctua- 
tions in  turbidity,  provision  should  be  made  for  the  introduction  of 
chemicals  into  the  raw-water  main,  across  the  center  of  the  basin, 
and  at  the  outlet  to  same,  and  the  point  of  introduction  should  be 
varied  with  the  condition  of  the  raw  water. 

The  chemicals  should  be  thoroughly  mixed  with  the  raw  water, 
but  violent  agitation  in  mixing  is  to  be  avoided,  as  tending  to 
break  up  the  flakes  of  coagulum.  Sufficient  mixture  is  generally 
provided,  where  the  chemicals  enter  the  raw-water  main  one  hun- 
dred feet  or  more  from  the  sedimentation  basin,  by  the  agitation 
due  to  the  flow  through  the  pipe.  At  some  plants  especially 
baffled  mixing  chambers  are  provided  in  connection  with  the 
sedimentation  basins.  Mixture  can  be  obtained  across  the  center 
of  the  basin  by  means  of  a  baffle  or  submerged  weir  to  contract  the 
area  of  flow  at  the  point  where  the  chemicals  are  introduced. 
After  the  reaction  has  taken  place,  the  flow  of  the  water  should  be 
as  smooth  as  possible,  as  the  flakes  of  coagulum  are  broken 
up  by  violent  agitation,  such  as  occurs  in  aerating  pipes  or  weirs. 


164  WATER   PURIFICATION    PLANTS 

The  lines  leading  from  the  orifice  box  to  the  point  of  introducing 
the  chemicals  into  the  water  to  be  treated  should  be  short  and  as 
straight  as  possible.  Relatively  large-sized  pipe  should  be  used  to 
prevent  clogging.  For  lime  or  soda-ash  solutions  black  wrought- 
iron  pipe  is  very  satisfactory.  Galvanized  pipe  should  be  avoided. 
For  aluminum  or  iron  sulphate  as  well  as  for  hypochlorite  solutions 
standard  weight  lead  pipe  is  fairly  efficient.  Bronze,  rubber,  or 
fiber  pipes  are  sometimes  used.  It  is  important  that  there  be  no 
air  traps  in  the  coagulant  lines.  These  should,  if  possible,  have  a 
uniform  downward  grade  toward  the  point  of  discharge,  and  near 
the  orifice  box  should  connect  into  a  vent  pipe,  to  allow  the  air 
entrapped  with  the  solution  to  escape. 

Comparison  of  Costs.  On  Plate  IX  have  been  plotted  the 
cost  of  each  of  the  methods  of  treatment  described,  for  various 
amounts  of  coagulant,  and  also  the  cost  of  removing  various 
amounts  of  acids.  The  cost  of  chemicals  includes  freight,  un- 
loading and  cartage,  deterioration,  and  the  rehandling  in  charging 
the  chemical  tanks.  The  costs  per  hundred  pounds  used  were: 
aluminum  sulphate,  $1.10;  ferrous  sulphate,  $0.70;  lime,  $0.35; 
soda  ash,  $1.00.  For  large-sized  plants  these  values  could  be  re- 
duced. From  these  curves  it  is  evident  that  the  iron  and  lime 
treatment  is  cheapest,  followed  by  alum  and  natural  alkalinity, 
alum  and  lime  (sufficient  to  produce  no  CO2),  alum  and  soda  ash, 
while  alum  and  soda  ash  (no  CO2)  is  most  expensive.  It  is  also 
evident  that  by  increasing  the  amount  of  lime  used  with  the  iron, 
the  cost  of  this  process  may  rise  above  that  of  alum  and  lime. 
The  iron-lime  treatment  is  slightly  more  effective  for  high  tur- 
bidities, a  fact  not  brought  out  by  these  curves.  For  acid  re- 
moval, lime  is  by  far  the  cheapest  reagent. 

Sterilization.  While  properly  treated  and  filtered  water  is 
practically  free  from  bacteria,  it  has  of  late  years  become  cus- 
tomary to  treat  the  filtrate  with  a  germicide  as  an  additional  pre- 
caution. Such  treatment  should  be  considered  solely  as  an 
added  safeguard,  and  under  no  condition  should  reliance  be  placed 
on  it  to  the  extent  of  neglecting  any  detail  in  the  process  of  filtra- 
tion. Bacterial  counts  of  the  filtrate  should  be  made  before 
applying  the  germicide  and  the  plant  efficiency  based  on  these. 
Counts  should  also  be  made  after  sterilization  to  measure  the 
effectiveness  of  the  agent  used. 

Hypochlorite  of  lime  has  been  very  extensively  used  for  this 


COAGULATION   AND   STERILIZATION  165 

purpose.  Liquid  chlorine  is  coming  into  use.  Sodium  hypo- 
chlorite,  electrolytically  prepared,  and  ultra-violet  rays  have  been 
used  experimentally  and  show  promise  of  future  development; 
ozone. and  copper  sulphate  have  also  been  tried. 

Hypocblorite  of  Lime.  Hypochlorite  of  lime  (CaCl2,Ca(OCl)2) , 
known  commercially  as  "  chlorid  of  lime  "  or  "  bleach/'  contains 
about  70  per  cent  of  a  mixed  salt  (calcium  chlorid  and  calcium 
hypochlorite) ,  and  30  per  cent  of  impurities,  such  as  lime  and 
water  of  hydration.  It  is  obtainable  in  canisters  of  from  100  to. 
750  pounds  each.  If  kept  exposed  to  the  air,  it  loses  strength 
through  absorption  of  water  and  volatilization. 

It  is  soluble  in  water  (about  1  part  in  20),  separating  into  its 
two  component  salts: 

CaCl2,Ca(OCl)2  =  CaCl2+Ca(OCl)2 

The  calcium  chlorid  is  inactive,  but  the  calcium  hypochlorite 
reacts  with  the  free  or  half-bound  carbonic  acid  in  the  water, 
giving  hypochlorous  acid  and  calcium  carbonate: 

Ca(OCl)2+H2CO3  =  2HOCl+CaCO3 
or  Ca(OCl)2+H2CO3CaCO3  =  2HOCl+2CaC03 

The  hypochlorous  acid  is  unstable,  and  readily  gives  up  its  oxygen 
to  organic  matter: 

2HOC1  =  2HC1+2O 

This  oxygen,  being  in  the  atomic  or  nascent  state,  is  very  active 
and  is  the  effective  germicide.  The  hydrochloric  acid  (HC1) 
formed  reacts  with  the  calcium  carbonate  (CaCO3)  formed  in  the 
previous  reaction,  reverting  it  into  carbonic  acid  again: 

CaC03+2HCl  =  H2C03+CaCl2 

These  reactions  and  the  germicidal  effect  are  also  obtained  in  the 
absence  of  carbonic  acid,  but  more  slowly.  The  time  required 
for  the  completion  of  the  reaction  is  variable,  being,  under  the  best 
conditions,  about  30  minutes,  but  increasing  as  the  temperature  of 
the  water  decreases  and  also  being  longer  in  waters  containing  only 
half-bound  carbonic  acid  than  in  those  containing  free  carbonic 
acid. 

Through  established  (although  illogical)  commercial  usage,  the 
oxidizing  strength  of  the  hypochlorite  is  measured  in  terms  of 
"  available  chlorine/'  that  is,  the  amount  of  chlorine  which  be- 


166  WATER   PURIFICATION   PLANTS 

comes  available  on  decomposing  chlorid  of  lime  with  a  strong  acid. 
This  may  be  computed  when  the  percentage  of  pure  bleach  is 
known,  as  follows: 

Available  chlorine  =  0. 56 X  percentage  of  pure  bleach.  Thus 
for  the  average  commercial  product  containing  68  per  cent 
CaCl2,Ca(OCl)2  the  "  available  chlorine"  is  0.56X. 68  =  38  per 
cent.  Only  half  of  the  "  available  chlorine  "  is  liberated  by  the 
weak  carbonic  acid  or  0.28  of  the  pure  bleach  or  "  calcium  oxy- 
chlorid."  The  actual  oxygen  liberated  is  22.5  per  cent  of  the 
"  available  chlorine." 

The  amount  of  available  chlorine  required  to  sterilize  the 
water  varies  with  the  amount  of  organic  matter  present  and  with 
the  turbidity  of  the  water.  It  is  best  determined  by  running  bac- 
terial counts  on  the  treated  water  and  using  the  minimum  dose 
that  will  insure  a  practically  sterile  water.  In  the  absence  of  bac- 
terial tests  or  as  a  check,  the  "  Test  for  Excess  of  Hypochlorite  of 
Lime,"  in  Chapter  III,  may  be  used.  Generally  M  to  }/2  part 
per  million  of  available  chlorine  is  sufficient,  although  sometimes 
more  is  required.  This  is  especially  true  if  the  water  contains  un- 
oxidized  organic  matter  or  ferrous  salts.  In  one  instance  it  was 
necessary  to  use  2  parts  per  million  of  available  chlorine,  any  re- 
duction being  followed  by  an  increase  in  the  typhoid-fever  rate. 
Ordinarily  so  large  an  amount  of  hypo  would  have  resulted  in  a 
very  strong  taste  in  the  water,  but  in  this  case  the  water  was  treated 
before  being  delivered  to  a  large  impounding  reservoir,  the  pro- 
longed storage  reducing  the  taste  considerably.  'One  part  per 
million  available  chlorine  is  equal  to  about  25  pounds  of  bleach 
per  million  gallons.  A  very  common  dose  is  8  pounds  of  bleach 
per  million  gallons.  For  treating  filtered  water  5  pounds  is  often 
sufficient. 

Hypochlorite  exerts  a  selective  action  on  the  bacteria  in  the 
water,  readily  destroying  such  pathogenic  species  as  B.  typhosus, 
the  cholera  spirillum,  and  the  like,  while  the  harmless  spore-forming 
varieties  are  affected  to  a  much  less  extent. 

The  chlorid  of  lime  is  introduced  into  the  water  as  a  solution 
in  a  manner  similar  to  coagulants  (see  Figs.  10  and  11).  As  it 
is  not  very  soluble  (about  1  part  in  20  of  water),  a  weak  solution 
should  be  used.  This  has  the  further  advantages  of  decreasing 
the  corrosive  action  on  piping  and  (in  the  case  of  small  plants) 
giving  a  quantity  of  solution  large  enough  to  be  accurately  mea- 


COAGULATION   AND    STERILIZATION  167 

sured  by  an  orifice  box  of  the  usual  type.  For  large  plants  a  2  per 
cent  solution  may  be  used,  for  smaller  plants  a  1  or  J/2  Per  cent 
solution  is  more  readily  handled.  It  is  often  an  advantage  to  make 
up  a  stronger  "  stock  "  solution,  containing  about  6  per  cent 
of  bleach  (approximately  2  per  cent  "  available  "  chlorine),  and 
dilute  this  as  required  to  the  standard  strength. 

In  making  up  solutions  care  should  be  taken  to  use  sufficient 
water,  as  if  made  into  a  thick  paste  the  bleach  dissolves  with 
difficulty.  Use  at  least  %  gallon  of  water  per  pound  of  bleach. 
It  should  also  be  remembered  that  a  large  amount  of  sludge 
is  formed,  and  as  part  of  the  available  chlorine  is  retained  by  this 
an  additional  allowance  must  be  made.  The  chlorine  in  the  sludge 
may  be  recovered  by  agitating  the  sludge  in  water  and  using  this 
water  in  mixing  up  a  fresh  batch,  although  the  extra  labor  and 
inconvenience  involved  hardly  justify  this  procedure. 

The  apparatus  used  in  preparing  the  solution  generally  con- 
sists of  a  small  mixing  or  "  pasting  "  tank  and  two  larger  solution 
tanks.  The  pasting  tank  is  located  above  the  solution  tanks 
(see  Fig.  11),  and  is  equipped  with  horizontal  mixing  paddles  and 
sometimes  with  rollers,  motor  driven,  for  grinding  and  mixing  the 
bleaching  powder  into  a  paste  with  water.  Two  screened  over- 
flows are  provided  near  the  top  of  the  tank,  one  to  each  solution 
tank,  as  well  as  a  hose  or  water  connection.  The  solution  tanks 
are  provided  with  motor-driven  stirring  paddles  and  with  piping 
connections  to  the  orifice  boxes.  These  pipes  should  tap  into  the 
tanks  somewhat  (6  to  9  inches)  above  the  bottom  to  avoid  the 
sludge  that  accumulates  on  the  bottom  of  the  tanks.  Ample 
drain  pipes  should  be  provided  to  remove  this  sludge  to  a  sewer. 
The  tanks  are  best  made  of  concrete  or  iron  and  piping  of  pure 
wrought  iron  (black)  or  lead.  Orifice-box  fittings  are  well  made 
of  acid-proof  bronze.  Wood  is  readily  attacked  by  the  solutions, 
and  if  used  should  be  painted  with  asphaltum  or  mineral  bitumi- 
nous paint.  The  same  is  true  of  copper  or  ordinary  brass. 

The  preparation  of  a  solution  is  best  illustrated  by  a  concrete 
example.  Assume  that  it  is  desired  to  treat  5,000,000  gallons  per 
day  with  0.4  part  per  million  available  chlorine,  using  33J/£  per 
cent  bleach  (which  may  be  taken  as  an  average  value  where  no 
analyses  are  made).  Referring  to  Plate  X,  and  using  the  dashed 
line  labeled  0.4  part  per  million  available  chlorine,  it  will  be  seen 
that  51  pounds  of  chlorid  of  lime  per  day  are  required.  The 


168  WATER    PURIFICATION    PLANTS 

dashed  line  is  so  drawn,  as  to  compensate  for  the  bleach  lost  in  the 
sludge,  using  a  1  per  cent  solution.  Assuming  a  day's  supply  of  1 
per  cent  solution  is  to  be  made  up  in  solution  tank  No.  1  (No.  2 
being  in  use  at  the  time),  weigh  out  51  pounds  of  bleach  into  the 
pasting  tank,  add  a  small  amount  of  water,  and  start  the  mixing 
paddles.  Slowly  add  water  until  the  tank  contains  at  least  J/2 
gallon  for  each  pound  of  bleach  (or  about  25  gallons,  preferably 
somewhat  more) .  Allow  the  paddles  to  mix  the  bleach  into  a  paste 
(which  requires  about  15  to  3D  minutes),  and  in  the  meantime  drain 
tank  No.  1  of  sludge.  Now,  with  the  mixing  paddles  still  in  mo- 
tion, turn  a  stream  of  water  into  the  pasting  tank  so  that  the  solu- 
tion is  slowly  flushed  into  the  solution  tank  through  the  overflow. 
Each  solution  tank  should  be  equipped  with  a  float  gage  reading 
directly  the  number  of  gallons  in  the  tank.  Allow  the  stream  in 
the  pasting  tank  to  continue  until  the  paste  is  all  flushed  out  and 
the  solution  tank  contains  the  amount  of  water  necessary  to  make  a 
1  per  cent  solution.  Referring  to  Plate  XI  (using  the  dashed  line 
to  allow  for  loss  in  sludge),  note  that  51  pounds  of  chemical  require 
620  gallons  of  water  to  make  a  1  per  cent  solution. 

After  the  requisite  amount  of  solution  has  been  made  up, 
the  stirrer  in  the  solution  tank  is  started  and  the  whole  thoroughly 
and  uniformly  mixed.  The  solution  is  then  allowed  to  settle  for  at 
least  one  hour,  and  preferably  longer,  after  which  a  sample  is  taken 
off  and  tested  for  available  chlorine  as  described  in  the  chapter  on 
chemical  tests.  If  a  slight  discrepancy  is  found  it  is  generally 
sufficient  to  adjust  the  orifice  opening  slightly  and  correct  future 
solutions  accordingly.  When  tank  No.  2  has  run  out,  No.  1  may 
now  be  put  into  service.  Care  must  be  taken  not  to  disturb  or 
agitate  the  solution  while  the  tank  is  in  service,  nor  must  it  con- 
tinue in  service  after  the  sludge  line  near  the  bottom  is  reached. 
By  adhering  to  the  instructions  here  given,  tastes  in  the  treated 
water  can  be  largely  avoided. 

Plate  XI  can  be  used  for  any  chemical  solution.  In  deter- 
mining the  gallons  of  water  for  any  strength  of  solution,  use  the 
solid  lines  for  clear  solutions  such  as  of  aluminum  or  ferrous  sul- 
phate, and  the  dashed  lines  for  solutions  which  leave  a  sludge 
such  as  lime  and  hypochlorite.  The  heavy  vertical  lines  give  the 
amount  of  solution  which  will  discharge  through  circular  orifices  of 
the  sizes  noted  under  6  inches  head  in  24  hours.  Never  use  a 
quantity  of  solution  less  than  will  require  an  orifice  of  J/£  inch 


COAGULATION   AND    STERILIZATION  169 

diameter  (200  gallons  per  day),  as  this  is  about  the  practical 
limitation  in  size. 

The  bleach  may  be  applied  to  the  raw,  settled,  or  filtered  water. 
It  is  least  effective  applied  to  the  raw  water,  and  is  difficult  to 
apply  to  the  filtrate  in  such  a  manner  as  to  get  uniform  distri- 
bution, since  it  must  generally  be  discharged  into  the  individual 
effluent  pipes  from  the  filters  into  the  clear- water  basin.  Such  a 
distribution  is  readily  obtained  by  applying  it  to  the  water  in  the 
latter  part  of  the  settling  basin  by  means  of  a  perforated  pipe.  It 
may  thus  be  given  15  to  30  minutes  for  reaction  before  the  water 
reaches  the  filters.  This  has  the  added  advantages  that  most 
of  the  taste  caused  by  the  hypochlorite  will  be  removed  by  adsorp- 
tive  action  in  the  filters,  as  well  as  keeping  the  filter  sand  sterilized 
and  preventing  "  after-growths  "  of  bacteria  in  the  sand  and 
underdrains. 

Water  which  has  been  treated  with  hypochlorite  very  often 
has  an  unpleasant  taste,  suggestive  of  iodoform.  There  are 
several  possible  reasons  for  this  taste.  Probably  the  action  of  the 
hypochlorite  on  organic  matter  is  partially  accountable  for  it. 
Since  the  rate  of  pumpage  varies,  whereas  the  solution  of  hypo  is 
generally  applied  uniformly,  and  since  the  solution  itself  may  vary 
in  strength,  due  both  to  stratification  and  to  variations  in  the 
bleaching  powder,  the  water  is  possibly  overdosed  at  times.  If 
adequate  storage  is  not  given  after  treatment,  the  water  may 
reach  the  consumer  before  the  reaction  is  complete,  especially  in 
winter,  when  it  is  sluggish. 

In  general,  taste  may  be  reduced  by  automatically  propor- 
tioning the  flow  of  hypo  to  the  pumpage,  by  mixing  the  solutions 
well  to  prevent  stratification,  by  tests  of  the  solution  to  determine 
the  available  chlorine,  and  by  storage  after  treatment  sufficient  for 
the  reaction  to  be  completed  (a  minimum  of  30  minutes).  The 
taste  may  be  removed  chemically  by  applying  sodium  thiosulphate 
(Na2S2O3,  5H2O),  in  amount  half  as  much  as  the  bleach,  15  to  30 
minutes  after  the  bleach  has  been  added.  This  will  remove  the 
taste  completely,  with  no  deleterious  effect  on  the  water,  at  an 
additional  cost  of  about  half  as  much  as  the  bleach.  It  can  be 
added  as  a  dilute  solution  by  means  of  a  solution  tank  and  orifice 
box.  The  addition  of  the  thiosulphate  stops  the  germicidal 
action  of  the  bleach  at  once,  which  is  the  reason  for  adding  it 
sufficiently  later  to  allow  the  bleach  to  destroy  the  bacteria. 


170 


WATER   PURIFICATION   PLANTS 


Liquid  Chlorine.  Chlorine  gas  liquefied  by  pressure  has  re- 
cently found  application  as  a  sterilizing  reagent.  Its  germicidal 
effect  results  from  the  same  cause  as  does  that  of  chlorid  of  lime, 

namely,  the  liberation 
of  nascent  oxygen  in  so- 
lutions. The  reactions 
are  as  follows: 


=  HOC1  +  HC1 
HOC1  =  HC1+O 

The  hydrochloric  acid 
formed  reacts  with  the 
carbonates  and  bicar- 
bonates  in  the  water  to 
form  chlorids  and  car- 
bonic acid,  thus: 

2HCl  +  CaCO3,H2CO3  = 
CaCl2+2H2CO3 

The  reaction  is  simpler 
than  in  the  case  of 
chlorid  of  lime  and  pro- 
ceeds readily  without 
the  presence  of  carbonic 
acid.  As  the  gas  is 
practically  pure,  and  is 
therefore  essentially  100 
per  cent  "  available 
chlorine,"  only  about 
one-third  as  much  is 
required  by  weight  as 

of  bleach.  Thus,  instead  of  12  pounds  per  million  gallons  of 
chlorid  of  lime,  4  pounds  of  the  gas  may  be  used,  or  instead  of 
5  pounds  (in  the  case  of  filtered  water),  1%  pounds  of  the  gas  may 
be  substituted.  Efficiency  in  operation  may  increase  this  ratio 
to  1  to  5  or  6. 

The  commercial  gas  is  99.8  per  cent  pure  chlorine  and  can  be 
purchased  in  steel  cylinders  8  inches  in  diameter  and  60  inches 


Courtesy  Electro-Bleaching  Gas  Company. 

FIG.  76. — Automatic  Liquid  Chlorine 
Apparatus. 


COAGULATION   AND   STERILIZATION  171 

high  containing  100  pounds  of  chlorine.  The  pressure  in  the 
cylinders  varies  with  the  temperature,  ranging  from  50  to  100 
pounds  per  square  inch. 

The  apparatus  used  for  introducing  the  chlorine  gas  into  the 
water  takes  a  variety  of  forms.  One  type  is  shown  in  Fig.  76. 
Two  cylinders  of  chlorine  gas  are  connected  through  a  manifold 
into  a  single  pipe.  To  this  pipe  is  attached  a  gage  to  indicate  the 
initial  pressure  in  the  cylinders.  The  gas  is  then  passed  through 
an  automatic  pressure-reducing  valve  which  maintains  a  constant 
pressure  regardless  of  the  decrease  in  quantity  of  gas  in  the  cylin- 
ders or  variations  of  temperature.  The  gas  then  passes  through  a 
second  adjustable  reducing  valve  by  which  any  desired  pressure 
may  be  maintained  over  an  orifice  plate  in  the  pipe  line.  The 
reducing  valves  perform  the  same  function  that  the  float  valve 
does  in  an  orifice  box  measuring  a  chemical  solution.  The  orifice 
allows  a  constant  quantity  of  gas  to  discharge  through  a  pipe  into 
an  absorption  tower,  through  which  a  constant  stream  of  water  is 
flowing.  This  water  absorbs  the  gas  and  carries  it  to  the  water 
supply  to  be  treated.  A  second  gage  is  generally  provided  to 
measure  the  pressure  on  the  orifice.  Piping,  valves,  gages,  etc., 
must  be  of  special  design  and  material  to  withstand  the  corrosive 
action  of  the  gas. 

The  convenience  and  simplicity  of  operation  as  compared  to 
chlorid  of  lime  are  obvious.  The  annoyance  of  dust  and  fumes  is 
done  away  with,  and  the  floor  space  occupied  is  greatly  reduced. 
The  cost  per  pound  is  about  six  times  that  of  bleaching  powder, 
but  as  the  strength  is  about  three  times  as  great,  and  as  it  can  be 
more  effectively  applied,  the  cost  of  chemical  required  is  less  than 
2  to  1.  Despite  this  fact,  and  in  view  of  the  decreasing  cost  of 
liquid  chlorine,  it  is  finding  much  favor. 

Sodium  Hypochlorite.  Sodium  hypochlorite  is  obtained  by 
passing  an  electric  current  through  a  solution  of  common  salt 
(sodium  chlorid).  Its  germicidal  effect  is  the  same  as  that  of 
calcium  hypochlorite,  resulting  from  the  liberation  of  nascent 
oxygen.  The  preparation  of  it  is  free  from  the  disagreeable  fea- 
tures attending  the  use  of  bleaching  powder,  and  there  is  no  lime 
sludge  to  dispose  of..  The  process  is  comparatively  new  and  not 
well  known  in  the  water-works  field,  and  the  apparatus  is  still  in 
the  formative  stage.  With  electric  current  below  1J^  cents  per 
kilowatt  hour,  and  salt  (second  grade)  at  J^  cent  a  pound  or  less, 


172 


WATER    PURIFICATION    PLANTS 


this  process  should  compete  on  favorable  terms  with  either  bleach- 
ing powder  or  liquid  chlorine. 

The  apparatus  used  is  shown  in  Fig.  77.  It  consists  essentially 
of  a  tank  for  holding  salt  solution,  an  orifice  box  for  measuring  the 
solution,  and  an  electrolytic  cell.  Referring  to  Fig.  78,  it  is  seen  that 
the  cell  consists  of  a  soapstone  or  porcelain  box,  about  28  inches 


Brine  Solution  Tank 


Thermometer 


II 
1  1 

Electrolytic 

u 

Cell                    jj 

To  Water  Supply 


TIG.  77. — Apparatus  for  Electrolytic  Preparation  of  Sodium  Hypochlorite. 
FIG.  ?8— Electrolytic  Cell. 

long,  12  inches  wide,  and  12  inches  deep,  having  at  each  end  a  baffle 
of  the  same  material  reaching  nearly  to  the  bottom.  Between 
these  end  baffles  are  spaced  a  number  of  carbon  plates  (in  this  case 
23),  which,  together  with  the  glass  partitions  above  and  below, 
divide  the  cell  into  24  compartments.  Alternate  partitions  have 
the  glass  baffles  perforated  with  an  opening  above  and  below  the 
carbon,  so  that  in  passing  through  the  cell  the  salt  solution  takes 


COAGULATION   AND    STERILIZATION  173 

the  circuitous  path  indicated  by  the  arrows.  Current  enters  and 
leaves  the  cell  through  two  carbon  electrodes,  one  at  each  end. 
Of  the  intermediate  carbons,  one  face  acts  as  the  positive  and  the 
other  as  the  negative  pole,  so  that  the  whole  device  is  really  made 
up  of  24  cells  in  series. 

When  a  direct  current  is  passed  through  these  cells,  and  a 
brine  solution  is  fed  into  them,  sodium  is  liberated  at  one  pole  and 
chlorine  at  the  other.  The  sodium  combines  with  the  water  to 
form  sodium  hydroxid  and  hydrogen.  The  sodium  hydroxid 
combines  with  the  chlorine  to  form  sodium  hypochlorite.  The 
hydrogen  gas  escapes.  The  reaction  may  be  represented  by  the 
symbols : 

NaCl+H2O  =  NaOCl+H2 

There  are,  however,  several  auxiliary  reactions  which  decrease 
the  amount  of  sodium  hypochlorite  formed  as  well  as  increase 
the  current  consumption.  Among  these  are  the  oxidation  of  the 
sodium  hypochlorite  to  sodium  chlorate,  and  its  reduction  to 
sodium  chlorid  by  the  liberated  hydrogen. 

Practically,  the  voltage  required  is  about  4  volts  per  cell;  for 
instance,  the  apparatus  described  above  would  require  a  voltage  of 
24X4,  or  96  volts,  consequently  the  ordinary  110- volt  current  could 
be  used  in  connection  with  a  rheostat.  Theoretically  it  requires 
1.23  kilowatt  hours  of  current  and  1.65  pounds  of  salt  to  produce 
1  pound  of  available  chlorine.  However,  as  the  best  cells  have  an 
energy  efficiency  of  only  about  25  per  cent,  and  not  more  than  20 
per  cent  of  the  chlorine  present  as  chlorid  is  converted  into  hypo- 
chlorite, it  actually  requires  at  least  5  amperes  of  current  and  over 
8  pounds  of  salt  per  pound  of  available  chlorine. 

In  practice,  the  salt  is  dissolved  in  water  to  a  strength  of  about 
a  10  per  cent  solution,  and  is  fed  gradually  to  the  electrolyzer  by 
means  of  a  siphon  connection  from  the  orifice  box.  The  tem- 
perature in  the  electrolyzer  should  be  kept  under  100°  Fahr. 
Lower  temperatures  give  better  results.  The  overflow  from  the 
electrolyzer  is  fed  into  the  water  to  be  treated,  either  directly  or 
through  an  equalizing  tank.  The  available  chlorine  in  the  effluent 
of  the  electrolyzer  is  determined  by  the  test  for  available  chlorine 
given  in  Chapter  III,  and  is  adjusted  by  regulating  the  orifice 
feed. 


174 


WATER   PURIFICATION   PLANTS 


Ultra-Violet  Rays.  The  ultra-violet  rays  from  an  electric 
mercury  vapor  lamp  have  a  direct  bactericidal  action,  not  only  on 
bacteria  in  the  active  but  also  in  the  spore  state,  which  resists 
vigorous  boiling.  It  is  necessary  that  the  lamp  be  enclosed  in  a 
quartz  tube,  as  ordinary  glass  is  opaque  to  these  rays.  Also  the 


Mercury  Lamp  «?    «?  Quartz  Lens 


Courtesy  Scientific  American. 

FIG.  79. — Ultra-Violet  Ray  Apparatus. 

water  must  be  brought  close  to  the  lamp,  in  order  to  make  the 
treatment  effective,  and  the  rays  must  be  applied  after  filtration, 
as  any  turbidity  cuts  them  off  very  quickly.  The  water  is  run 
through  a  cast-iron  box,  in  the  top  of  which  is  suspended  a  quartz 
mercury  arc  lamp  enclosed  in  a  box  with  quartz  sides,  to  prevent 
the  water  striking  the  lamp,  Fig.  79.  The  cast-iron  box  is  baffled 
so  as  to  bring  the  water  close  to  the  lamp.  An  electrically  operated 
valve  placed  in  the  line  ahead  of  the  apparatus  and  in  series  with 
the  lamp  serves  to  by-pass  the  water  in  case  the  lamp  becomes  in- 
operative. A  series  of  such  apparatus  is  necessary,  as  each  lamp  can 
only  take  care  of  about  150,000  gallons  per  day.  This  method  has 
been  in  use  at  Marseilles,  France,  since  1910.  It  has  also  been 
employed  in  the  United  States  in  sterilizing  bottled  water.  Its  use 
in  large  purification  plants  has  been  proposed,  and  it  is  probable 
that,  with  more  efficient  apparatus,  its  application  will  become 
practicable  where  electric  current  is  cheap.  It  has  the  advantages 
of  being  tasteless  and  easy  of  application. 

Copper  Sulphate.  The  use  of  copper  sulphate  for  destroying 
algae  in  reservoirs  has  been  noted  in  Chapter  V.  It  has  also  been 
found  that  10  parts  per  million  of  copper  sulphate  will  kill  typhoid 
and  colon  bacilli.  Attempts  have  been  made  to  produce  a  mixed 
salt  of  ferrous  and  copper  sulphates  containing  about  1  per  cent 
of  the  latter.  Such  a  coagulant  was  used  with  some  success  at 


COAGULATION   AND    STERILIZATION 


175 


Copper 


Wire 


^Pulley 


Funnel 
To  Raw  Water'til 

I 


FIG.  80. — Automatic  Coagulant  Control  for  a  Small  Plant 


From  "Apparatus  for  Water  Purification  Plants,"  by  Thomas  Fleming,  Jr.  Jour.  Eng.  Soe. 
Penna.,  June,  1911. 

FIG.  81. — Coagulant  Regulating  Device  at  Monessen,  Pa. 


176  WATER   PURIFICATION    PLANTS 

Marietta,  0.,  where  a  bacterial  efficiency  of  99.33  per  cent  was 
obtained.  A  small  amount  of  copper  was  found  in  the  effluent 
of  the  niters,  attributable  to  the  brass  strainers  used. 

Ozone.  Ozone,  produced  electrolytically,  has  been  used  for 
sterilizing  water.  Although  it  has  been  extensively  experimented 
with  for  a  number  of  years,  it  has  as  yet  found  very  little  practi- 
cal application  and  seems  a  less  logical  successor  to  chlorid  of 
lime  than  liquid  chlorine,  sodium  hypochlorite,  or  ultra-violet 
rays. 

Automatic  Regulation  of  Coagulation.  One  of  the  most  useful 
automatic  devices  with  which  any  plant,  large  or  small,  can  be 
equipped  is  an  apparatus  for  proportioning  the  amount  of  coagulant 
solution  to  the  varying  raw-water  flow.  Any  such  device  involves 
a  means  for  measuring  the  raw-water  flow  and  some  method  of 
having  this  affect  one  of  several  variables  which  control  the  flow  of 
the  coagulant  solution  from  the  orifice  box,  namely,  the  area  of 
orifice  opening,  or  the  head  over  the  orifice. 

Fig.  80  shows  a  device  of  this  nature,  which  has  been  success- 
fully used  in  institutional  and  other  small  plants.  The  orifice  box 
is  of  the  standard  float-controlled  type,  being  fed  from  a  coagulant 
solution  tank  in  the  usual  manner.  Instead  of  an  orifice,  the 
outlet  from  the  orifice  box  consists  of  a  small  brass  tube  nipple  to 
which  a  glass  tube  is  attached  by  means  of  a  short  piece  of  rubber 
hose,  making  a  flexible  joint.  The  glass  tube  is  bent  at  the  end, 
and  discharges  into  a  funnel,  whence  the  coagulant  solution  flows 
through  a  pipe  to  the  raw-water  main.  The  raw  water,  on  its  way 
to  the  settling  basin,  flows  through  a  weir  box,  which  is  the  re- 
quired measuring  device  in  this  case.  There  is  a  float  in  this 
weir  box,  and  from  it  a  wire  or  cord  runs  over  pulleys  and  is 
attached  to  the  glass  tube.  When  the  flow  of  raw  water  decreases, 
the  water  level  in  the  weir  box  falls,  and  the  float  with  it.  This 
exerts  a  pull  on  the  wire  and  raises  the  glass  tube,  thereby  de- 
creasing the  flow  of  coagulant.  Similarly  with  an  increased  raw- 
water  pumpage  the  float  rises,  causing  the  end  of  the  glass  tube  to 
be  lowered,  thereby  increasing  the  flow  of  coagulant. 

Fig.  81  shows  an  automatic  coagulant  regulating  device 
suitable  for  a  larger  plant.  In  this  case  the  apparatus  is  mounted 
in  a  small  house  directly  upon  the  coagulation  basin,  which  hap- 

*  Engineering  Record,  LIII,  p.  392. 


COAGULATION    AND    STERILIZATION 


177 


pens  to  be  a  large  round  steel  tank.  The  raw  water  is  pumped 
through  the  inlet  pipe  into  a  large  box.  In  this  it  flows  through  a 
perforated  baffle  and  out  through  an  orifice  in  the  bottom  of  the 
box.  The  coagulant  orifice  boxes  are  attached  directly  to  the  raw- 
water  orifice  box,  and  are  of  rather  deep  proportion  with  glass 
fronts.  The  coagulant  solution  is  pumped  from  solution  tanks 
below  up  into  the  orifice  boxes  which  are  provided  with  over- 
flows, the  surplus  pumpage  overflowing  and  running  back  into 
the  solution  tanks  by  gravity.  These  overflows  have  a  telescoping 
joint  and  are  hung  from  cords  passing  over  differential  pulleys  and 
leading  to  a  barrel  float  in  the  raw-water  orifice  box.  An  increase 
in  pumpage  causes  the  water  level  in  the  raw-water  orifice  box  to 


/Pivot 


FIG.  .82. — Coagulant  Controller  for  a  Large  Plant. 

rise,  carrying  the  barrel  float  up  with  it.  This,  acting  through  the 
counterweight  and  differential  pulley,  raises  the  overflow  funnels, 
and  consequently  the  water  level  in  the  coagulant  orifice  boxes, 
increasing  the  flow  of  coagulant  solution. 

Fig.  82  shows  diagrammatically  the  principle  of  one  of  several 
patented  devices  used  in  large  filtration  plants.  The  raw  water  is 
measured  by  means  of  a  Venturi  meter  or  other  constriction  in  the 
pipe.  The  water  levels  at  the  inlet  and  at  the  throat  of  the  tube 
are  carried  to  the  float  tubes  A  and  B.  Due  to  the  increased  veloc- 
ity of  the  water  through  the  throat,  the  water  level  in  tube  B  is 
lower  than  that  in  tube  A  by  a  distance  h',  which  increases  as  the 


178 


WATER    PURIFICATION    PLANTS 


flow  through  the  meter  increases.  It  is  evident  that  under  action 
of  the  floats  A  and  B  alone  the  pivoted  walking  beam  would  be 
tilted  downward  at  the  right-hand  end.  This  causes  the  valve  in 


Courtesy  of  the  Roberta  Filter  Manufacturing  Co. 

FIG.  83.— Constant  Feed  Orifice  Box. 

the  line  from  the  solution  tank  to  the  float  tube  C  to  open,  ad- 
mitting coagulant  solution  until  the  upward  force  due  to  the 
submergence  of  float  C  is  sufficient  to  bring  the  walking  beam 
level.  This  closes  the  valve  in  the  coagulant  line.  The  water 


COAGULATION   AND    STERILIZATION  179 

level  in  tube  C  is  communicated  to  the  orifice  box,  the  discharge 
of  which  varies  with  this  water  level. 

Fig.  83  shows  an  orifice  box  designed  for  use  where  the  raw- 
water  pumpage  is  constant,  which  combines  a  number  of  useful 
features.  It  consists  of  an  enameled  iron  tank  (1),  containing  a 
float  valve  (3),  fed  from  the  coagulant  solution  tank  through  the 
pipe  and  valve  (2).  The  water  level  in  the  tank  is  maintained 
at  a  constant  height  by  the  glass  float  (4).  The  orifice  is  an  ad- 
justable needle  valve  (5).  The  discharged  solution  falls  into  a 
perforated  cup  (9),  and  from  this  into  the  funnel  (6),  which  con- 
nects to  a  pipe  leading  to  the  raw  water.  It  will  be  noted  that  the 
cup  (9)  is  suspended  from  a  spring.  Any  variation  in  the  orifice 
discharge,  due  either  to  the  clogging  of  the  orifice  or  to  the  failure 
of  the  float  valve  to  operate  properly,  causes  the  weight  of  this  cup 
to  vary,  thereby  extending  or  contracting  the  spring  and  closing 
the  electrical  contact  (8).  This  causes  the  bell  (12)  to  ring, 
warning  the  operator  that  the  orifice  box  is  not  acting  properly. 
The  bell  may  be  shut  off  by  opening  the  switch  (11)  when  the 
orifice  box  is  not  in  use.  A  drain  (7)  is  provided,  as  well  as  a 
flushing  connection  (10),  to  which  a  pressure  pipe  may  be  attached 
for  cleaning  out  the  coagulant  discharge  line. 

There  are  numerous  other  methods  of  accomplishing  the  same 
results,  all  based  on  the  principles  above  outlined. 


CHAPTER  VII 

WATER-SOFTENING 

IT  is  sometimes  desirable  to  soften  a  water  as  well  as  filter  it, 
and  for  this  purpose  the  mechanical  filter  plant  is  well  adapted 
with  a  few  modifications.  Essentially  these  modifications  con- 
sist of: 

a.   Larger  sedimentation  basins. 

6.    Facilities  for  mixing  the  lime  with  the  water. 

c.    Increased  facilities  for  handling  lime  and  soda  ash. 

Larger  sedimentation  capacity  is  necessary  to  allow  sufficient, 
time  for  the  reaction  between  the  lime  and  the  bicarbonates  in 
the  water,  thereby  avoiding  to  a  large  extent  deposits  of  calcium 
carbonate  on  the  grains  of  the  filter  sand,  and  in  the  filter  piping 
and  mains.  The  time  for  the  reaction  depends  on  the  constituents 
in  the  water,  on  the  adequacy  of  mixing  the  lime  with  the  water, 
on  the  design  and  condition  of  the  basins,  and  on  the  temperature. 
A  sedimentation  period  of  from  10  to  12  hours  fulfils  average 
conditions,  although  at  times  a  period  of  4  hours  may  be  sufficient. 
These  periods  are  based  on  the  total  capacity  of  the  basins.  Water 
containing  large  amounts  of  magnesium  salts  requires  a  longer 
period  for  reaction.  Generally  the  same  is  true  of  attempts  to 
soften  waters  which  are  not  very  hard  to  begin  with. 

The  thorough  mixture  of  the  slaked  lime  with  the  water  is 
extremely  important.  This  may  be  accomplished  in  several  ways. 
The  lime  emulsion  may  be  added  to  the  raw  water  shortly  before  it 
reaches  the  mixing  chamber.  It  should  be  introduced  into  the 
raw-water  main  through  several  pipes  entering  at  points  a  number 
of  feet  apart,  since  the  lime  emulsion  is  not  very  soluble,  and  if 
introduced  at  one  point  would  sink  to  the  bottom  of  the  main  and 
badly  choke  same.  The  mixing  chamber  in  this  case  is  divided 
by  vertical  baffles  into  compartments  about  3  feet  wide,  causing 
the  water  to  travel  up  over  one  baffle  and  down  under  the  next  at 
about  1  foot  per  second  velocity.  By  providing  mixing  chambers 
of  this  type  of  half  an  hour's  capacity,  a  very  thorough  mixture  of 
the  lime  emulsion  and  the  water  is  obtained,  and  the  softening 

180 


WATER-SOFTENING  181 

reactions  are  greatly  accelerated.  Another  method  of  accom- 
plishing the  same  result  is  that  described  in  connection  with  the 
Columbus  filtration  plant  (Chapter  II).  There  the  raw  water  is 
divided  into  three  parts.  Twenty-five  per  cent  of  it  is  led  to  a 
number  of  saturation  chambers,  where  the  total  dosage  of  lime  is 
added  to  it,  and  it  is  thoroughly  mixed  by  means  of  revolving 
paddles.  Another  25  per  cent  is  dosed  with  soda  ash  in  another 
compartment.  These  two  portions  are  then  returned  to  the  re- 
maining 50  per  cent  of  untreated  water,  and  the  whole  is  run 
through  a  mixing  chamber  of  the  type  already  described. 

The  sedimentation  basins,  besides  being  of  the  capacity  above 
stated,  should  be  so  designed  as  to  give  the  water  a  velocity  of 
from  2.5  to  3.0  feet  per  minute.  They  should  be  well  baffled,  so 
as  to  prevent  shortcircuiting  of  the  water.  There  seems  to  be 
some  advantage  in  having  a  small  amount  of  sludge  present  in  such 
*a  manner  that  the  water  passing  through  comes  in  contact  with  it, 
as  this  seems  to  promote  precipitation  of  the  carbonates. 

With  water  at  a  low  temperature  a  longer  sedimentation  period 
is  required  than  with  a  warmer  water,  this  following  from  the 
laws  of  chemical  reaction. 

The  need  for  larger  lime  and  soda  tanks,  pipes,  conveyers,  and 
storage  facilities  is  evident,  in  that  from  five  to  ten  times  as  much 
of  these  chemicals  must  be  handled  as  in  ordinary  filtration. 
Methods  of  dry  feeding  such  as  were  described  in  connection  with 
the  Columbus  plant  become  almost  imperative  in  the  larger  in- 
stallations. 

The  meaning  of  the  term  "  hardness,"  the  constituents  pro- 
ducing this  quality,  and  the  properties  imparted  by  their  presence 
to  the  water,  have  been  discussed  in  the  chapter  on  the  "  Inter- 
pretation of  Tests."  The  chemical  constituents  causing  this 
quality  may  be  recapitulated  in  another  manner,  as  shown  on 
following  page. 

The  bicarbonates  of  calcium,  magnesium,  and  iron  constitute 
temporary  hardness,  being  removed  by  boiling  or  precipitated 
by  lime.  The  sulphates,  chlorids,  and  nitrates  (together  with  a 
small  residue  of  the  normal  carbonates)  of  calcium  and  magnesium 
cause  permanent  hardness,  not  being  removed  by  boiling,  but 
being  precipitated  as  calcium  and  magnesium*  carbonate  upon  the 

*  Magnesium  carbonate  is  somewhat  soluble,  but  is  precipitated  by 
additional  lime. 


182 


WATER   PURIFICATION   PLANTS 


Hardness 


Alkalinity 


Mineral 
acidity 


Bicarbonates  of 

Carbonates  of 
Hydroxids  of 


[  Sulphates 

Incrustants       j  Chlorids 
Nitrates 


of 


{Sulphuric  acid 
Sulphates  of 


Calcium  (Ca) 

Magnesium  (Mg) 

Iron  (Fe) 

Calcium 

Magnesium 

Calcium 

Magnesium 

f  Calcium 
\  Magnesium 


Iron  (Fe) 
Aluminum  (Al) 


addition  of  soda  ash.  Bicarbonate  of  iron  occurs  in  some  waters, 
and  may  be  considered  as  temporary  hardness. 

The  question  of  the  degree  of  hardness  permissible  is  one  of 
locality  to  a  large  extent.  A  central  State  water  which  passes 
without  comment  would  seem  extremely  hard  to  a  visitor  from 
New  England.  Considering  the  economic  aspect  of  the  question 
as  regards  soap  consumption  and  the  formation  of  boiler  scale  in 
addition  to  the  personal  equation,  it  would, seem  that  softening 
may  be  regarded  as  unnecessary  with  water  of  a  temporary  hard- 
ness from  75  to  100  parts  per  million  or  less,  the  exact  value  de- 
pending somewhat  on  the  additional  permanent  hardness  present. 
The  value  of  permanent  hardness  at  which  softening  may  rationally 
be  considered  is  approximately  50  parts  per  million.  In  other 
words,  the  question  of  water-softening  may  be  profitably  con- 
templated when  the  total  (temporary  +  permanent)  hardness  of  a 
water  reaches  150  parts  per  million.  On  the  other  hand,  it  is  neces- 
sary to  neutralize  mineral-acid  hardness,  even  when  present  only 
in  small  amount,  owing  to  its  corrosive  action.  A  few  rivers  re- 
ceiving much  mine  drainage  have  a  mineral  acidity  of  over  20 
parts  per  million. 

There  is  a  lower  limit  beyond  which  softening  should  not  be 
attempted.  This  may  be  placed  at  from  50  to  60  parts  per  mil- 
lion. Due  to  limitations  in  the  accuracy  of  applying  the  lime  and 
soda  solutions,  and  vagaries  in  the  reactions  of  softening,  at- 
tempts to  work  to  a  lower  limit  would  result  in  caustic  water  at 
times,  and  this  would  lead  to  trouble  with  after-precipitation,  and 


WATER-SOFTENING  183 

to  complaints  from  the  consumers,  due  to  the  greater  hardness  of 
the  caustic  water,  and  to  its  objectionable  taste.  Small  plants, 
where  regulation  is  not  very  efficient,  had  better  limit  themselves 
to  a  total  hardness  of  75  in  the  effluent.  It  is  questionable  whether 
extremely  soft  waters,  even  when  naturally  so,  are  as  healthful  as 
waters  containing  more  natural  salts  in  solution  (especially  cal- 
cium salts).  Investigations  seem  to  show  that  in  regions  with 
fairly  hard  waters,  the  inhabitants  are  larger  and  less  susceptible 
to  dental  and  bone  diseases.*  Researches  made  by  Messrs.  Olaf 
Bergem  and  P.  B.  Hawk,  University  of  Illinois,  seem  to  show  that 
water  rendered  caustic  by  lime  treatment  has  an  inhibitive  action 
on  the  digestive  processes.  This  applied  particularly  to  water 
containing  magnesium  hydroxid  after  treatment,  and  was  attri- 
buted to  the  adsorptive  action  of  this  substance  in  colloidal  form 
on  the  saliva.  This  action  is  stronger  the  more  recently  the  water 
has  been  softened. 

Reactions  of  Water- Softening.     The    reactions   between   the 
lime  and  the  bicarbonates  in  the  water  are  as  follows: 

1.  CO2+Ca(OH)2  =  CaCO3+H2O 

2.  CaCO3H2CO3+Ca(OH)2  =  2CaCO3+H2O 

3.  2NaHCO3+Ca(OH)2  =  CaCO3+Na2CO3+2H2O 

4.  MgCO3H2CO3+2Ca(OH)2  =  2CaCO3+Mg(OH)2+2H2O 

The  lime  seems  to  attack  the  constituents  of  the  water  in  the 
order  given.  First  the  free  carbonic  acid  is  removed,  then  re- 
spectively the  bicarbonates  of  calcium,  sodium,  and  magnesium. 
Note  that  twice  as  much  lime  is  used  for  precipitating  the  bicar- 
bonate of  magnesium,  as  the  carbonate  is  soluble  and  must  be 
converted  into  the  insoluble  hydroxid.  The  precipitated  calcium 
carbonate  is  somewhat  soluble  (about  30  p. p.m.),  so  that  it  is  im- 
possible (as  well  as  undesirable)  to  remove  hardness  entirely. 

The  removal  of  permanent  hardness  is  accomplished  by  the 
following  reactions  for  calcium  salts: 


CaSO4       ) 

(    Na2S04j 

1 

CaC],        [  +N 

^CO3  =  1  2NaCl 

-  +CaCO3 

Ca(N03)2  ) 

(  2NaNO3  ! 

1 

*Berg,  Biochemische  Zeitschrift,  v.  24,  p.  282  (1910);  v.  26,  p.  204  (1910). 
Rose,  Deutsche  Monatschrift  f.  Zahnheilkunde,  1904-1908. 


184  WATER   PURIFICATION    PLANTS 


The  similar  reactions  for  magnesium  salts  are  : 


MgS04       ) 

MgCl2        f  +  Na2CO3+Ca(OH).,=      2NaCl        +  CaCO3+Mg(OH)2 

Mg(N03)2  )  (  2NaN03 

In  neutralizing  acid  water  the  reactions  are  : 


The  sodium  carbonate  is  added  to  remove  the  calcium  sulphate 
formed  by  the  reaction  of  the  acid  or  sulphate  with  the  calcium 
hydroxid. 

Special  Tests  in  Water-  Softening.  The  necessary  tests  to 
determine  the  amounts  of  lime  and  soda  ash  required  in  water- 
softening  are: 

1.  Free  carbonic  acid. 

2.  Half  -bound  carbonic  acid  (44  per  cent  of  the  bicarbonates). 

3.  Total  magnesium. 

4.  Incrustants. 

The  tests  for  free  carbonic  acid  and  bicarbonates  were  given  in 
detail  in  the  chapter  on  tests.  The  tests  for  magnesium  and 
incrustants  follow. 

Total  Magnesium:  *  Apparatus.  Six-inch  porcelain  dish,  one 
25-cc.  pipette,  one  150-cc.  measuring  flask,  Bunsen  burner. 

Reagents.  ^  sulphuric  acid,  a  clear,  saturated  solution  of  lime- 
water,  erythrosin,  and  phenolphthalein. 

Procedure.  The  solution  of  lime-water  is  made  by  adding 
pure  calcium  oxid  to  boiled  distilled  water  in  quantity  sufficient 
to  leave  a  residue  of  undissolved  lime  after  vigorous  shaking. 
Allow  the  solution  to  stand  until  all  undissolved  lime  has  settled  out. 
Test  the  strength  of  the  lime-water  by  carefully  measuring  out 
25  cc.  and  titrating  with  ^  sulphuric  acid  using  phenolphthalein. 
Determine  the  alkalinity  to  erythrosin  of  a  sample  of  the  water  to 
be  tested.  Take  another  100-cc.  sample  of  the  water  and  pour 
into  a  6-inch  porcelain  dish.  Add  the  same  amount  of  ^5  sul- 
phuric acid  as  was  used  in  the  alkalinity  test,  which  should  make 
it  neutral  to  erythrosin.  Boil  down  to  a  volume  of  30  to  40  cc.  to 
expel  the  free,  half-bound,  and  bound  carbonic  acid. 

Introduce  25  cc.  of  clear  saturated  solution  of  the  lime-water 
into  a  150-cc.  measuring  flask,  glass-stoppered.  While  still  hot, 

*  "  Standard  Methods  of  Water  Analysis."     A.  P.  H.  Assoc. 


WATER-SOFTENING  185 

transfer  the  contents  of  the  porcelain  dish  to  this  flask,  and  rinse 
the  dish  several  times  with  hot  distilled  water,  pouring  the  rinsings 
into  the  flask,  and  make  up  the  solution  to  about  2  cc.  above  the 
150-cc.  line  in  the  flask.  Mix  well,  stopper  immediately,  and 
cool  until  the  precipitated  magnesium  hydrate  has  completely 
settled  out.  Pipette  off  50  cc.  of  the  clear  solution,  using  care  not 
to  disturb  the  precipitate,  and  run  into  a  porcelain  dish.  Titrate 
with  ~  sulphuric  acid  to  phenolphthalein  until  neutral. 

If  C  represents  the  number  of  cc.  of  ^  sulphuric  acid  required 
to  neutralize  25  cc,  of  the  lime-water,  and  N  the  number  of  cc.  of 
the  same  acid  used  in  the  final  titration,  then  the  magnesium 
(Mg)  in  parts  per  million  equals  2.4  (C-3N). 

Incrustants.*  Under  this  name  are  included  the  sulphates, 
chlorids,  and  nitrates  of  lime  and  magnesium  which  cause  per- 
manent hardness. 

Apparatus.  500 -  cc.  Jena  glass  Erlenmeyer  flask,  200 -cc. 
graduated  flask,  100-cc.  measuring  glass,  glass  filter  funnel  and 
filter  paper,  Bunsen  burner. 

Reagents,  f^  soda  reagent  (equal  parts  NaOH  and  Na2C03), 
^  sulphuric  acid,  erythrosin,  boiled  distilled  water. 

Procedure.  Measure  200  cc.  of  the  water  into  the  Jena  glass 
flask;  boil  10  minutes  to  expel  the  carbonic  acid  and  add  25  cc.  of 
the  soda  reagent.  Boil  down  to  100  cc.,  cool,  rinse  into  200  cc. 
graduated  flask,  and  make  up  to  200  cc.  with  boiled  distilled  water. 
Filter,  rejecting  the  first  50  cc.  and  titrate  100  cc.  of  the  filtrate, 
using  ^  sulphuric  acid  and  erythrosin.  Take  25  cc.  of  the  soda 
reagent  and  titrate  with  ^  sulphuric  acid  and  erythrosin.  If 
S  =  the  cc.'s  of  ^  sulphuric  acid  (H2S04)  required  to  neutralize 
25  cc.  of  soda  reagent,  and  N=  cubic  centimeters  of  ^  sulphuric 
acid  (H2SO4)  required  to  neutralize  the  100-cubic-centimeter 
sample  of  the  filtrate,  the  incrustants  in  parts  per  million  (as 
calcium  carbonate)  equal  12.5  (S-2N). 

Treatment.  From  the  above  reactions  it  will  be  seen  that 
in  order  to  remove  the  temporary  hardness,  it  is  necessary  to  add 
enough  lime  to  react  with  the  carbonic  acid,  the  bicarbonates,  and 
an  additional  amount  for  the  magnesium  salts,  so  that  they  may 
be  precipitated  as  magnesium  hydroxid.  Sodium  bicarbonate 
(Equation  3),  while  not  causing  hardness,  must  be  removed,  if 

*  "  Standard  Methods  of  Water  Analysis."     A.  P.  H.  Assoc. 


186  WATER   PURIFICATION   PLANTS 

present,  before  the  magnesium  compounds  will  be  attacked.     The 
amounts  of  85-per-cent  lime  required  for  this  purpose  are  : 


10  parts  per  milHm  of:  . 

Free  and  half  -bound  CO2  125  pounds 

Magnesium  (total)  224  pounds 

The  amount  of  97-per-cent  soda  ash  required  to   remove  the 
incrustants  is: 


10  parts  per  mtUIOn  of: 

Incrustants  as  CaCO3  91  pounds 

In  neutralizing  acid  hardness  (measured  as  H2S04),  use  the 
following  amounts: 

10  parts  per  million  of:  Require  per  million  gallons: 

H2SO4  (disregarding  formation  of  CaSO4)     56  pounds  85  per  cent 

CaO 
To  remove  incrustants  (CaSO4)  formed        94  pounds  97  per  cent 


Example  1.  A  typical  "  hard  "  water  analyzing: 

Turbidity,  150  parts  per  million 

Free  CO2,  10  parts  per  million 

Erythrosin  alkalinity,  150  parts  per  million 

Phenolphthalein  alkalinity,  0  part  per  million 

Incrustants,  95  parts  per  million 

Magnesium,  21  parts  per  million 

Referring  to  Plate  II,  it  is  seen  that  all  the  alkalinity  is  in  the 
form  of  bicarbonates.  The  half-bound  CO2  therefore  is  44  per 
cent  of  150  or  66  p.p.m.  The  alum  required  is  found  from  Plate 
III,  using  the  medium  curve,  to  be  1  grain  per  gallon,  or  143  pounds 
per  million  gallons.  Referring  to  Plate  IV,  the  amount  of  lime 
required  for  no  increase  in  CO2  is  .35  grain  per  gallon,  or  50  pounds 
per  million  gallons.  The  combined  (free  and  half-bound)  C02 
is  10+66  =  76  parts  per  million. 

The  amount  of  lime  required  is: 

To  react  with  alum  50  pounds  per  million  gallons 

For  free  and  half-bound  CO2  — 

7.6X125  950  pounds  per  million  gallons 

For  total  magnesium  —  2.1X224    470  pounds  per  million  gallons 
Total  lime  (85  per  cent  CaO)    =  1,470  pounds  per  million  gallons 


WATER-SOFTENING  187 

The  amount  of  soda  ash  required  is: 
To  react  with  incrustants — 

9.5X91  =    865  pounds  per  million  gallons 

Example  2.  A  typical  acid-water  analyzing: 

Turbidity,  10     parts  per  million 

Free  CO2,  10     parts  per  million 

H2SO4  acidity,       22     parts  per  million 
Iron,  1.5  parts  per  million 

Incrustants,          81.4  parts  per  million 
Magnesium,  6.7  parts  per  million 

From  Plate  VI,  a  turbidity  of  10  requires  0.4  grain  per  gallon  of 
ferrous  sulphate.  Referring  to  Plate  VIII,  it  will  be  seen  that  the 
iron  present  together  with  some  of  the  acidity  is  just  sufficient  to 
supply  the  coagulation  required,  so  that  no  ferrous  sulphate  need 
be  added. 

The  lime  required  is: 

For  free  CO2,  1 X 125  =  125  pounds  per  million  gallons 

For  H2SO4  acidity,  2.2  X  56  =  124  pounds  per  million  gallons 
For  total  magnesium,  0.67X224=  150  pounds  per  million  gallons 
Total  lime  (85  per  cent  CaO),  399  pounds  per  million  gallons 

The  soda  ash  required  is: 

For  H2SO4,  acidity,  2.2X94=  207  pounds  per  million  gallons 

For  incrustants,  8.14X91  =  741  pounds  per  million  gallons 

Total  soda  ash  (97  per  cent),  948  pounds  per  million  gallons 

In  these  examples  sufficient  soda  and  lime  have  been  added  to 
react  with  all  the  hardening  constituents  of  the  water.  This  is 
not  always  desirable,  as  under  many  conditions  it  is  more  eco- 
nomical to  remove  only  part  of  these.  For  instance,  if  the  water 
contains  a  large  amount  of  bicarbonates  of  calcium  and  sodium 
and  a  relatively  unimportant  quantity  of  magnesium  salts,  the 
last  could  not  be  removed  until  all  the  calcium  and  sodium  bi- 
carbonates had  been  precipitated.  This  would  mean  that  much 
of  the  lime  would  be  required  to  remove  the  sodium  bicarbonate, 
which  is  not  objectionable.  In  such  a  case  it  might  be  more 
economical  to  add  only  enough  lime  to  react  with  the  bicarbonate 
of  calcium. 

To  determine  the  most  economical  treatment,  test  the  raw 
water  for  free  and  half-bound  carbonic  acid,  incrustants,  and 
magnesium,  and  compute  the  amounts  of  lime  and  soda  ash  needed 


188  WATER   PURIFICATION   PLANTS 

for  their  complete  removal.  Then  take  ten  half -gallon  bottles, 
each  containing  a  quart  of  the  raw  water,  and  add  proportions  of 
lime  and  soda  from  one-tenth  to  the  full  amount  required  for 
complete  removal  of  hardening  constituents.  Shake  well,  and 
allow  to  stand  for  24  hours.  Then  analyze  the  contents  of  each 
bottle  for  alkalinity  and  incrustants  to  determine  the  reduction  in 
hardness.  In  this  way  determine  the  proportions  and  amounts, 
giving  a  maximum  reduction  with  the  use  of  a  minimum  of 
chemicals. 

Introduction  of  Coagulants.  The  point  of  introduction  of 
the  coagulants  (aluminum  or  iron  sulphate)  deserves  special  con- 
sideration in  water-softening.  During  the  progress  of  the  soften- 
ing reaction,  the  final  products,  calcium  carbonate  and  magnesium 
hydroxid,  are  present  in  the  water  in  quantities  above  the  satura- 
tion value.  This  follows  because  the  water  is  always  in  contact 
with  precipitated  calcium  carbonate  and  magnesium  hydroxid,  and 
because  of  the  tendency  of  these  substances  to  form  through  the 
reaction  of  the  slaked  lime  and  bicarbonates  present  in  the  water. 
The  result  is  that  the  water  is  a  supersaturated  solution  of  these 
compounds,  and  furthermore  contains  them  in  a  finely  divided 
state  of  incipient  precipitation  akin  to  a  colloidal  solution,  which 
gives  to  the  water  what  may  be  called  an  artificial  turbidity. 
Anything  which  will  destroy  this  condition  of  unstable  equilibrium 
and  hasten  precipitation  will  materially  shorten  the  reaction 
period  of  the  softening  process.  Passing  the  water  over  cakes  of 
calcium  carbonate  or  violently  agitating  the  water  (especially  in 
contact  with  sand)  are  two  methods  of  bringing  this  about. 
Better  than  either  is  the  addition  of  a  coagulant.  It  is  found  that 
one  grain  of  aluminum  sulphate  will  reduce  the  alkalinity  of  lime- 
treated  water  30  parts  per  million,  instead  of  7  to  8,  as  the  theoret- 
ical reaction  would  indicate.  This  action  is  mechanical  as  well 
as  chemical.  It  is  therefore  advisable  to  add  some  coagulant  to 
the  treated  water  as  it  leaves  the  mixing  chamber.  It  sometimes 
happens  that  the  water  becomes  quite  clear  in  the  settling  basins 
before  it  reaches  the  filters.  In  that  case,  a  small  amount  of 
coagulant  should  be  added  to  the  water  as  it  leaves  the  settling 
basins,  in  order  that  there  may  be  sufficient  precipitate  in  the 
water  to  form  a  good  mat  on  the  filters.  It  may  be  added  that 
magnesium  hydroxid  itself  is  a  flocculent  precipitate  and  acts  as_a 
coagulant  at  times. 


CHAPTER  VIII 

SEDIMENTATION 

THE  purposes  of  sedimentation  are:  a,  to  allow  the  suspended 
and  coagulated  matter  to  settle  out  of  the  water;  6  to  allow  time 
for  the  complete  reactions  of  the  coagulating  chemicals;  c,  by  (a) 
and  (6),  to  relieve  the  filters  of  a  large  amount  of  work  (at  least  80 
per  cent),  and  to  reduce  the  washing  of  the  filters  to  a  minimum; 
d,  to  act  as  an  equalizing  basin  for  the  raw-water  pumpage,  thereby 
keeping  the  load  on  the  filters  uniform. 

The  time  required  for  the  settling  out  of  the  suspended  matter 
is  a  variable  quantity,  depending  chiefly  on  the  size  and  specific 
gravity  of  the  suspended  particles.  To  a  less  extent  it  is  affected 
by  the  nature  of  the  particles,  by  the  temperature  of  the  water, 
and  by  its  chemical  constituents.  Where  sedimentation  is  pre- 
liminary to  filtration  a  period  of  2  to  6  hours  is  generally  allowed. 
Where  coagulation  and  sedimentation  constitute  the  final  process 
the  period  should  be  from  one  to  three  days. 

The  time  for  completion  of  reactions  varies  with  the  chemicals 
used,  their  concentration,  thoroughness  of  mixing,  and  the 
natural  qualities  and  temperature  of  the  water.  Alum  and  iron 
reactions  are  quite  rapid,  rarely  requiring  more  than  30  minutes, 
but  the  reaction  of  lime  with  the  bicarbonates  of  the  water  is  slow, 
and  may  require  12  hours. 

WTith  very  turbid  water  the  sedimentation  is  advantageously 
divided  into  two  stages:  a,  Plain  sedimentation,  to  remove  the 
heavy  suspended  matter;  b,  coagulation  and  sedimentation,  to 
remove  the  lighter  suspended  and  colloidal  matter.  This  point 
and  the  application  of  the  chemicals  have  been -more  fully  con- 
sidered in  the  chapter  on  Coagulation  and  Sterilization. 

Much  importance  attaches  to  the  proper  baffling  of  a  sedi- 
mentation basin,  in  order  to  prevent  the  water  from  following 
currents  or  short-cutting.  It  sometimes  happens  that  through 
improper  baffling  a  basin  designed  to  give  four  hours'  sedimentation 
Is  in  reality  allowing  the  water  to  pass  through  in  half  an  hour. 
The  raw  water,  being  drawn  from  near  the  bottom  of  a  river  or 

189 


190 


WATER    PURIFICATION    PLANTS 


lake,  is  always  of  maximum  density.  Assuming  an  unbaffled 
basin  or  one  of  type  shown  in  Fig.  84,  and  that  it  has  been  standing 
full  of  water  preliminary  to  starting,  so  that  the  water  has  been 
warmed  or  cooled,  according  to  season,  in  either  case  decreasing 


FIG.  84. 

its  specific  gravity,  the  raw  water  pumped  into  it  on  starting  will 
sink  and  flow  along  the  bottom  of  the  basin,  due  to  its  greater 
density.  This  tendency  to  sink  to  the  bottom  of  the  basin  is 


FIG.  85. 


increased  where  the  water  enters  the  basin  by  means  of  aerators, 
as  in  Fig.  84,  due  to  the  downward  velocity  imparted  thereby. 
The  water  flowing  along  the  bottom  causes  an  upward  displace- 


Stagnant 


FIG.  85. 

ment  of  the  lighter  water  in  the  basin  and  starts  a  current  near  the 
surface  toward  the  outlet.  With  no  baffle  in  the  basin  the  lighter 
water  would  gradually  be  removed  and  a  more  uniform  flow 
result,  but  with  the  very  common  central  baffle,  the  water  would 
form  the  currents  shown,  the  heavier  lines  representing  the  most 
rapid  flow,  and  a  large  portion  of  the  basin  would  be  ineffective. 
With  warmer  ground  water  the  flow  would  be  as  in  Fig.  85.  This 
is  not  as  bad,  as  the  quiescent  water  below  receives  the  sediment 


SEDIMENTATION 


191 


from  the  flowing  stratum  and  allows  it  to  settle,  whereas  in  Fig. 
84  the  water  tends  to  scour  the  sediment  from  the  bottom  and 
carry  it  to  the  filters  to  a  greater  extent. 

The  persistence  of  currents  once  formed  is  very  marked,  even 
after  the  difference  in  specific  gravity  or  the  initial  velocity  causing 
them  is  removed.  Thus  the  currents,  formed  in  types  of  Figs.  84 


FIG.  87. 


\ 
I 

T 


FIG.  88. 

and  85,  continue  after  the  temperature  of  the  water  is  equalized 
throughout,  as  determined  by  a  delicate  thermometer.  This 
persistence  is  also  shown  in  Fig.  86,  showing  the  very  common 
manner  of  introducing  the  raw  water  into  the  settling  basin  by  one 
or  more  horizontal  pipes.  Eddy  currents  are  set  up  thereby,  as 


192  WATER    PURIFICATION    PLANTS 

shown.  The  introduction  and  withdrawal  of  the  water  should  be 
done  with  as  little  agitation  or  velocity  as  possible,  either  by 
weirs,  or  grids  of  pipe  with  numerous  openings. 

Fig.  87  shows  a  satisfactory  arrangement  of  baffles  for  a  small 
rectangular  basin  with  aerator  inlets.  A  splasher  float  is  pro- 
vided below  the  aerators  to  break  the  fall  of  the  water.  The  baffles 
at  the  quarter  points  prevent  under-scour,  and  the  central  baffle 
breaks  up  surface  currents.  The  lower  four  feet  act  as  a  re- 
ceiving basin  for  sediment  settling  out  of  the  water  above. 

Fig.  88  shows  a  system  of  vertical  baffles  adapted  for  large 
basins. 

Every  effort  should  be  made  to  get  the  most  work  out  of  the 
basin,  by  proper  coagulation,  baffling,  and  cleaning,  as  in  this  way 
the  expense  of  operating  and  washing  the  filters  is  reduced.  Oc- 
casional bacterial  and  turbidity  tests  of  the  influent  and  effluent 
should  be  made,  to  determine  the  efficiency  of  sedimentation. 
A  properly  operated  basin  should  effect  a  removal  of  bacteria  and 
sediment  of  from  75  to  90  per  cent.  The  efficiency  depends  on  the 
area  and  depth  of  the  basin,  as  well  as  upon  the  turbidity  and 
amount  of  coagulation  in  the  water.  With  the  copious  precipitates 
obtained  in  water-softening,  in  conjunction  with  the  large  sedi- 
mentation basins  used,  it  is  possible  to  get  an  average  bacterial  re- 
moval of  98  per  cent.  The  effluent  from  the  basins  should  not  be 
entirely  clear,  but  should  have  a  visible  coagulation  corresponding 
to  a  turbidity  of  from  25  to  35. 

To  obtain  the  best  efficiency,  the  basins  must  be  cleaned  as 
frequently  as  conditions  require.  Generally  the  time  for  cleaning 
is  indicated  by  a  decrease  in  basin  efficiency,  due  to  some  of  the 
settled  silt  and  coagulant  being  swept  up  from  the  bottom  and 
carried  over  to  the  filters.  In  deep  basins  septic  action  may 
start,  evidenced  on  the  surface  by  the  appearance  of  gas  bubbles 
or  pieces  of  black  sludge.  In  warm  climates  the  formation  of 
algae,  slimes,  or  vegetative  growths  on  the  surface  makes  very  fre- 
quent cleaning  necessary. 

To  clean  a  basin,  it  should  be  drained,  and  the  accumulated 
sludge  swept  or  flushed  with  a  fire  hose  into  the  sewer, 


CHAPTER  IX 

FILTRATION  AND  GENERAL  OPERATION 

Routine  of  Operation.  To  operate  a  filter  plant  efficiently, 
certain  recurring  portions  of  the  work  should  follow  a  definite 
schedule.  The  operations  which  can  generally  be  so  arranged  are: 

a.  Making  of  tests. 

b.  Preparation  of  coagulant  solutions. 

c.  Inspections  of  plant. 

d.  Washing  of  filters. 

The  basis  of  the  routine  should  be  the  length  of  time  during  which 
the  men  work,  which  is  usually  8  or  12  hours,  but  may  be  a  variable 
quantity  in  the  case  of  small  plants,  which  are  shut  down  daily 
after  pumping  a  certain  required  quantity  of  water. 

Making  of  Tests.  In  plants  which  operate  only  a  portion 
of  the  day  the  tests  are  generally  made  before  starting  up  in  the 
morning,  and  in  some  cases  only  the  physical  and  chemical  tests 
are  run,  and  weekly  samples  are  taken  and  sent  to  a  competent 
bacteriologist  for  determination  of  the  bacterial  count  and  coli 
in  the  effluent.  A  more  rational  procedure  would  be  to  take 
the  raw-water  samples  before  starting,  the  settled-water  samples 
(at  the  outlet  of  the  basins)  after  an  interval  equal  to  the  actual 
time  required  for  the  water  to  pass  through  the  basins  (determined 
as  described  under  Calibration),  and  the  filtered- water  samples 
(from  the  effluent  sample  pumps)  after  an  interval  equal  to  the 
actual  time  required  for  the  water  to  pass  through  the  filters  and 
connecting  piping. 

In  plants  running  continuously  samples  are  generally  taken 
and  tests  made  sufficiently  before  the  end  of  a  shift  so  that  the, 
results  may  be  available  for  making  up  the  solutions  for  the 
coming  shift.  With  variable  raw-water  conditions  it  may  become 
necessary  to  make  tests  at  four-  or  even  two-hour  intervals,  but 
this  is  exceptional.  In  all  cases  there  is  an  advantage  in  allowing 
a  proper  time  interval  to  elapse  between  the  taking  of  raw-,  settled-, 
and  filtered-water  samples,  so  that  the  same  "  batch  "  of  water 
may  be  followed  through  the  whole  process. 

The  dosage,  chemical  and  physical  constitution  of  the  water  are 

193 


194  WATER   PURIFICATION   PLANTS 

continually  fluctuating  about  a  mean  value,  which  is  itself  varying 
in  a  more  uniform  manner,  so  that  the  samples  taken  at  even  two- 
hourly  periods  will  probably  depart  considerably  from  average 
conditions.  In  large  plants  where  economic  conditions  warrant 
the  effort,  it  may  be  well  to  take  samples  half-hourly  for  limited 
periods,  so  as  to  get  composite  results.  A  series  of  tests'  taken 
close  together,  two  or  three  times  a  year,  and  carefully  studied 
will  often  point  to  possible  improvements  in  the  methods  of 
applying  chemicals  and  the  coagulation  process  generally. 

Preparation  of  Coagulant  Solutions.  From  the  tests  and  with 
the  aid  of  the  charts  explained  in  the  chapter  on  Coagulation,  it 
is  possible  to  compute  the  pounds  of  coagulant  required  per 
million  gallons.  It  still  remains  to  ascertain  the  number  of 
million  gallons  to  be  pumped.  If  the  plant  is  not  equipped  with 
automatic  coagulant  regulation,  the  engineer  should  be  required  to 
inform  the  filter  operator  as  to  the  rate  at  which  he  intends  to 
pump  during  the  coming  shift  of  8  or  12  hours,  and  to  maintain 
this  rate  of  pumping  uniformly.  If  a  departure  from  the  fixed 
rate  becomes  necessary  during  the  shift,  the  pumping-station 
engineer  should  be  obliged  to  notify  the  filter-plant  operator,  so 
that  the  latter  can  make  the  necessary  adjustment  of  orifice  boxes, 
etc.  This  calls  for  means  of  measuring  the  rate  of  pumpage. 
With  direct-acting  pumps  this  is  most  readily  accomplished  by 
means  of  stroke  counters;  with  centrifugal  pumps,  by  means  of 
speed  counters  or  tachometers.  If  either  of  these  methods  is 
used,  the  pumps  should  be  recalibrated  frequently,  as  explained 
under  Calibration.  Devices  for  the  same  purpose,  which  are  less 
liable  to  variation,  are  Venturi  meters,  pitometers,  weirs,  and  ori- 
fices. If  possible,  a  permanent  measuring  device  of  one  of  these 
types  should  be  installed  in  the  raw-water  line,  with  indicators  in 
both  the  coagulant  house  and  pumping  station. 

The  amounts  of  chemicals,  as  determined  from  the  tests  and 
pumpage,  are  carefully  weighed  out  upon  a  platform  scale,  a 
separate  weighing  box  being  maintained  for  each  kind  of  chemical. 
In  large  plants,  where  conveyers  and  other  labor-saving  apparatus 
are  used,  automatic  hopper  or  other  special  scales  are  often  pro- 
vided for  the  chemicals. 

The  most  troublesome  and  wasteful  chemical  that  must  be 
handled  is  quicklime.  It  requires  considerable  labor  in  slaking, 
and  the  emulsion  clogs  pipes  and  is  particularly  troublesome  in 


FILTRATION   AND    GENERAL    OPERATION  195 

the  orifice  boxes,  much  lime  tending  to  settle  out,  due  to  the  small 
flow  through  the  orifice.  The  losses  result  principally  through 
carbonization  in  storage,  incomplete  slaking,  and  the  settling  out 
of  the  hydrate  when  applied  as  an  emulsion  to  the  raw  water,  due 
to  its  small  solubility  (only  the  portion  in  solution  takes  any  part 
in  the  reaction  with  the  alum  or  iron).  This  loss  may  amount  to 
from  25  to  50  per  cent.  To  reduce  losses  to  a  minimum,  it  is  neces- 
sary to  secure  high  calcium  lime  and  have  it  shipped  to  the  plant, 
where  small  amounts  are  used,  in  tight  barrels;  where  large 
amounts  are  used,  in  bulk,  in  tight  box  cars,  with  all  openings 
carefully  closed,  to  prevent  the  entrance  of  air  or  moisture.  Ar- 
riving at  the  plant,  if  in  barrels,  it  should  be  stored  in  a  dry  place; 
if  in  bulk,  in  covered  concrete  bins,  having  a  hopper  bottom, 
so  that  it  may  be  withdrawn  from  underneath  without  the  ad- 
mission of  air.  It  should  then  be  weighed  out  as  required,  and 
slaked  in  an  iron  slaking  box,  using  about  three  times  its  volume 
of  hot  water.  The  lime  should  be  mixed  with  the  water  until 
every  part  is  moistened,  but  should  not  be  stirred  while  slaking. 
Covering  the  box  to  conserve  the  heat  is  advantageous.  Two 
slaking  boxes  and  two  solution  tanks  should  be  used,  so  as  to 
allow  a  batch  to  be  slaked  during  the  previous  shift.  The  slaked 
lime  should  be  run  through  a  strainer  screen  into  the  solution  tank 
and  diluted  with  water  to  an  emulsion  of  the  consistency  of  milk. 
To  keep  a  uniform  concentration,  the  stirring  paddles  must  be 
kept  in  constant  motion  while  the  solution  is  being  used.  The 
connection  from  the  solution  tank  to  the  orifice  box  should  be  as 
short  and  straight  as  possible,  as  it  is  here  that  the  greatest  con- 
striction must  necessarily  occur.  The  orifice  box  should  receive 
frequent  attention,  to  see  that  the  lime  does  not  settle  therein  and 
the  orifice  does  not  clog.  The  discharge  line  from  the  orifice 
box  to  the  raw  water  should  be  as  short  and  straight  as  possible. 
The  strength  of  solution  should  be  kept  constant,  and  changes  in 
treatment  made  by  increasing  or  decreasing  the  orifice  opening. 
Thus,  with  a  sliding  orifice,  assuming  that  approximately  2  grains 
per  gallon  of  lime  are  to  be  used,  slake  the  proper  amount,  and 
dilute  with  enough  water  to  make  an  amount  of  emulsion  that 
will  last  just  one  shift  (8  to  12  hours),  with  the  orifice  at  a  mid- 
position.  Then  if,  owing  to  a  change  in  the  raw  water,  4  grains 
per  gallon  are  required,  open  the  orifice  twice  as  wide;  if  1  grain  is 
required,  close  the  orifice  to  half  the  initial  width. 


196  WATER   PURIFICATION    PLANTS 

Alum,  iron  sulphate,  and  soda  ash  should  be  dissolved  in  warm 
water  and  discharged  into  the  respective  solution  tanks  through 
strainer  screens.  The  solutions  should  have  a  strength  of  not  over 
6  per  cent.  The  stirring  paddles  need  only  be  run  until  the 
concentration  of  the  solutions  has  become  uniform.  To  prevent 
oxidation  of  the  iron  solution,  the  tank  should  be  covered  and 
stirring  reduced  to  a  minimum.  The  predetermined  amounts  of 
coagulant  should  be  used  in  making  up  solutions,  and  the  amount  of 
water  necessary  to  dilute  to  the  customary  strength  added.  Then 
the  orifice  should  be  set  to  pass  this  amount  of  solution  in  8  or  12 
hours,  as  the  case  may  be.  Any  sudden  variation  can  be  met  by 
opening  or  closing  the  orifice  proportionately.  The  number  of 
gallons  of  water  required  to  make  a  6  per  cent  solution  is  two 
times  the  pounds  of  coagulant;  for  a  3  per  cent  solution,  4  times 
the  pounds  of  coagulant. 

Besides  keeping  the  solutions  of  uniform  strength,  it  is  essential 
that  the  orifice  boxes  operate  properly.  This  involves  keeping 
a  constant  head  over  the  orifices  and  keeping  the  orifices  open  to 
full  size.  Small  particles  of  sediment  or  coagulant  lodging  in  the 
seat  of  the  float  valve  may  prevent  this  from  closing  and  result  in 
an  increase  in  head  over  the  orifice.  Coagulant  may  lodge  or 
crystallize  on  the  edges  of  the  orifice  and  especially  in  the  corners 
and  cause  a  marked  variation  in  flow. 

Hypochlorite  of  lime  is  relatively  insoluble,  and  its  resistance 
to  solution  is  increased  by  the  fact  that  it  tends  to  float  on  top  of 
the  water.  It  is  customary  to  mix  the  required  amount  in  a 
small  tub  provided  with  a  revolving  paddle,  so  that  it  can  be 
brought  into  intimate  contact  with  the  water,  and  then  empty 
this  solution  into  a  larger  tank,  where  it  is  diluted  with  water  to 
about  a  2  per  cent  solution.  The  fumes  from  the  dry  hypo  are 
very  corrossive,  especially  to  copper  and  brass,  and  it  is  well  to 
have  as  little  as  possible  exposed  to  the  air.  The  orifice  box 
should  be  made  with  as  little  brasswork  as  possible,  hard  rubber 
forming  a  good  substitute. 

Duplication  of  tanks,  orifice  boxes,  and  piping  is  very  essential 
in  this  part  of  the  plant,  as  with  a  breakdown  in  chemical  treat- 
ment a  satisfactory  effluent  is  not  possible. 

Regarding  the  storage  of  chemicals,  that  of  lime  has  been  con- 
sidered. The  remaining  should  be  stored  in  a  dry  place  con- 
venient of  access. 


FILTRATION   AND    GENERAL    OPERATION  197 

Ferrous  sulphate,  on  exposure  to  air  and  moisture,  oxidizes 
on  the  surface,  with  the  formation  of  ferric  sulphate  and  hydroxid. 
Therefore  it  should  be  stored  in  bins  with  a  minimum  exposure 
of  surface. 

Inspection.  Hourly  inspections  should  be  made  of  the  orifice 
boxes,  to  insure  their  feeding  the  coagulant  regularly,  and  to  guard 
against  stoppage.  The  solution  tanks  should  be  looked  after 
frequently,  to  see  that  the  mixing  paddles  are  in  operation  and 
the  solution  is  of  uniform  strength. 

The  same  may  be  said  with  regard  to  examining  the  coagu- 
lation of  the  raw  water  at  the  inlet  to  the  settling  basin  and 
on  the  filters.  This  is  best  done  by  collecting  a  sample  of  the 
water  in  a  clean,  clear  glass.  The  coagulation  should  be  plainly 
visible,  of  about  half  a  pin-head  in  size,  and  flocculent.  The 
settled  water  should  show  a  visible  coagulation  corresponding 
to  a  turbidity  of  about  25  to  35.  Should  it  be  excessively  turbid, 
if  aluminum  sulphate  is  being  used  alone,  increase  the  dose  or 
add  about  one-third  as  much  lime;  with  a  very  turbid  water,  try 
applying  part  of  the  coagulant  at  the  center  of  the  basin.  The 
excessive  turbidity  of  the  settled  water  may  also  be  caused  by 
sediment  being  swept  up  from  the  bottom  of  the  settling  basin, 
if  it  is  not  clean. 

Acid  waters  or  those  containing  ammonia,  organic  matter,  or 
alkalis  in  certain  concentration  give  trouble  with  colloidal  solu- 
tions of  the  coagulant,  especially  in  cold  weather.  Decreasing 
the  ratio  of  lime  to  alum  or  iron,  or  a  considerable  increase  in  the 
amount  of  chemicals,  is  often  effective  with  such  trouble. 

At  weekly  or  bi-weekly  intervals  each  filter  should  be  examined. 
This  is  best  done  just  previous  to  washing  the  filter.  The  points 
to  be  investigated  are: 

a.  The  condition  of  the  sand. 

b.  The  rate  of  washing  and  the  process  of  washing. 

c.  The  rate  of  filtration. 

d.  The  operation  of  the  effluent  controller. 

e.  The  operation  of  the  loss  of  head  gages. 

The  filter  to  be  examined  should  be  shut  down  and  the  water 
level  lowered  below  the  sand  line  by  opening  the  drain  valve. 
The  general  appearance  of  the  Schmutzdecke  should  be  noted,  and 
a  sample  of  sand  should  be  taken. 


198  WATER   PURIFICATION    PLANTS 

The  filter  should  then  be  washed.  During  this  process  the 
rate  of  washing  should  be  measured  as  explained  under  "  Calibra- 
tion." Any  unevenness  in  the  wash  distribution  should  be  noted. 
The  sand  should  be  lifted  over  the  whole  area  of  the  filter  bed. 
This  can  be  ascertained  by  thrusting  a  thin  pole  into  the  filter 
sand,  which  should  meet  no  obstruction  until  the  gravel  is  reached. 
A  cup  attached  to  a  stick  should  be  held  so  as  to  receive  the  over- 
flow from  the  wash-water  troughs,  and  the  samples  of  water  so 
obtained  should  be  examined  for  any  sand  which  might  be  carried 
over. 

After  washing,  the  water  should  again  be  drawn  down  to 
observe  the  effect.  There  should  be  no  patches  of  mud  left  on  the 
filter  sand,  although  a  uniform,  thin  film  of  coagulum  is  not  ob- 
jectionable. The  sand  surface  should  be  level  and  free  from 
bumps  or  hollows.  There  should  be  a  mark  placed  on  the  side 
of  the  filter  tank  at  the  sand  line,  and  note  should  be  taken  as  to 
whether  the  sand  is  settling  below  this  mark,  which  may  be  due  to 
the  sand  being  washed  away,  or  to  settling  in  the  under-drain 
system.  A  sample  of  the  sand  should  be  taken  and  examined  for 
incrustation  and  change  in  effective  size. 

The  rate  of  filtration  can  be  checked  as  explained  under 
"  Calibration."  By  taking  this  at  intervals  during  a  run  the 
working  and  accuracy  of  the  rate  controller  can  be  checked.  The 
correctness  of  the  loss-of-head  gages  can  be  ascertained  by  mea- 
surements of  the  actual  difference  in  level  between  the  water  on 
the  filter  and  in  the  effluent  pipe. 

In  connection  with  the  other  routine  work,  occasional  turbidity 
and  bacterial  tests  of  the  settled  water  will  shed  light  on  the 
efficiency  both  of  the  settling  basin  and  filters.  As  much  work  as 
possible  should  be  thrown  on  the  settling  basin,  as  this  prevents 
clogging  of  the  filters  and  reduces  the  amount  of  wash  water  re- 
quired. 

Operation  of  Filters.  The  ultimate  efficiency  of  the  plant  de- 
pends entirely  on  the  care  and  proper  manipulation  of  the  filters, 
no  matter  now  perfect  the  coagulation  or  sedimentation.  The 
maintaining  of  a  suitable  rate  of  filtration  is  most  important, 
owing  to  the  fact  that  the  coagulant  forms  a  gelatinous  mat  on 
the  surface  and  in  the  upper  part  of  the  sand,  which  forms  the 
real  medium  of  filtration,  and  which  is  broken  through  by  exces- 
sive velocities  of  the  water.  The  maximum  rate  with  alum 


FILTRATION   AND    GENERAL   OPERATION  199 

coagulation  usually  is  125,000,000  gallons  per  acre  per  day,  with 
iron,  100,000,000  gallons  per  acre  per  day,  corresponding  re- 
spectively to  2.0  and  1.6  gallons  per  square  foot  per  minute. 
Generally  the  filter  capacity  is  more  than  sufficient  and  a  lower 
rate  can  be  adopted.  The  load  should  be  distributed  among 
all  the  units  equally,  an  important  point,  often  neglected. 

Each  filter  unit  is  provided  with  a  rate  controller  on  the 
effluent  outlet,  the  purpose  of  which  is  to  maintain  automatically 
a  constant  rate  of  filtration  regardless  of  loss  of  head.  These 
controllers  are  provided  with  an  adjustment  by  which  they  may 
be  set  to  filter  at  any  desired  rate.  If  kept  clean,  and  given  the 
care  and  attention  required  by  any  automatic  device  of  this 
character,  they  will  function  properly  and  do  much  toward 
maintaining  a  uniform  distribution  of  load  among  the  units  and 
preventing  the  sudden  breakings-through  of  the  filter  mats,  with 
the  consequent  pollution  of  the  clear-water  basin  with  raw  water. 
Too  often  they  are  neglected  to  a  point  where  they  cease  to 
operate,  or  are  dismantled  by  the  operator,  rate  control  being  at- 
tempted by  manipulating  the  effluent  valves  so  as  to  maintain  a 
uniform  loss-of-head  reading  or  until  the  operator  feels  by  some 
unerring  instinct  that  the  right  rate  of  flow  is  attained.  This 
practice  cannot  be  too  severely  condemned,  and  the  same  can  be 
said  of  the  very  general  tendency  to  deprecate  other  automatic 
devices  and  gages  about  the  plant,  because  they  do  not  operate 
from  the  start  without  attention.  Such  devices  used  about  a 
filter  plant  are  very  simple  compared  to  those  used  successfully  in 
other  work,  and  their  imperativeness  reflects  strongly  on  the 
mechanical  ability  of  the  attendant.  In  rate  controllers,  proper 
care  generally  involves  keeping  bearings  and  sliding  joints  lubri- 
cated and  free  from  incrustation,  orifice  openings  clean  and  of 
full  size,  and  preventing  air  pockets. 

Rate  controllers  should  be  calibrated  occasionally  to  see  that 
they  are  correctly  set.  To  do  this,  close  the  influent  valve  and 
note  the  fall  in  water  level  over  the  whole  area  of  the  filter  unit 
in  half  a  minute.  Repeat  several  times  and  from  the  average 
drop  compute  the  quantity  of  water  in  cubic  feet,  which,  multiplied 
by  15,  gives  the  rate  in  gallons  per  minute.  Compare  this  with  the 
setting  of  the  controller,  which  correct  accordingly.  Repeat  for 
various  rates  and  for  each  filter  unit.  Check  the  regulation  of 
the  controller  by  noting  the  rate,  as  above,  with  different  heads 


200  WATER   PURIFICATION   PLANTS 

over  the  filter  sand,  or  vary  the  head  by  throttling  the  effluent 
valve. 

Each  filter  is  equipped  with  a  loss-of-head  gage,  to  measure  the 
friction  loss  through  the  mat,  sand,  gravel,  and  under-drain  system. 
When  operating  properly,  this  should  be  an  index  to  the  load  dis- 
tribution among  the  filters,  as  the  loss  of  head  should  increase 
uniformly  for  all,  and  to  the  time  for  washing  the  filter,  which 
should  be  done  whenever  the  loss  of  head  is  not  over  8  feet  greater 
than  the  initial  loss  of  head,  pertaining  when  the  filter  is  put  into 
commission  after  washing.  If  any  filter  shows  an  excessive  loss 
of  head  as  compared  with  the  rest,  under  normal  operating  condi- 
tions, it  is  a  sign  that  the  gravel  or  strainer  system  is  clogged  or 
obstructed. 

As  generally  constructed,  the  loss-of-head  gage  consists  of  two 
float  tubes,  one  connected  with  the  raw  water  above  the  sand,  the 
other  with  the  effluent  pipe.  The  difference  in  the  water  levels 
in  these  tubes  is  recorded  on  a  dial  by  means  of  floats  operating  a 
differential  gear.  The  gage  can  be  adjusted  to  read  correctly  by 
measuring  from  the  tops  of  the  tubes  the  distance  to  each  water 
level,  obtaining  the  difference  in  water  levels  by  subtraction,  and 
setting  the  pointer  of  the  gage  to  read  correctly  on  the  dial. 
Gages  which  operate  from  the  floats  by  means  of  wires  or  cords 
are  easily  thrown  out  of  adjustment  and  should  be  frequently 
checked  and  reset  if  necessary. 

The  effluent  pipe  from  each  unit  should  be  provided  with  a 
sampling  cock  or  pump,  so  that  frequent  individual  samples  can  be 
obtained  for  bacterial  and  turbidity  tests.  Any  filter  found  giving 
an  inferior  effluent  should  be  shut  down  at  once,  and  not  used  untilr 
the  cause  of  trouble  has  been  found  and  corrected.  If  the  water 
in  the  clear-water  basin  appears  cloudy,  more  alum  or  iron  should 
be  used;  if,  with  the  iron  treatment,  it  has  a  yellow  tint,  use  more 
lime.  A  porcelain  plate  placed  in  the  bottom  of  the  clear  well  and 
observed  from  a  dark  place  will  accentuate  any  cloudiness  or  dis- 
coloration. 

It  is  important  that  the  sand  and  gravel  be  kept  clean.  This 
can  generally  be  accomplished  by  washing  with  sufficient  water 
and  pressure.  If  the  wash  water  is  not  uniformly  distributed,  as 
will  occur  should  some  of  the  strainers  become  stopped  up,  certain 
portions  of  the  sand  will  accumulate  filth  indefinitely  and  become 
breeding-places  for  bacteria.  Similarly  in  a  poorly  designed  or 


FILTRATION   AND    GENERAL    OPERATION  201 

operated  filter,  mossy  growths  will  form  in  the  gravel  and  under- 
drains.  Such  conditions  will  manifest  themselves  on  inspection  of 
the  filter  after  washing  by  slimy,  obviously  unwashed,  patches  on 
the  sand  surface,  which  should  be  followed  up  by  digging  into  the 
sand.  Furthermore,  the  filtered  water  may  contain  bits  of  de- 
cayed moss,  or  have  a  higher  bacterial  count  than  the  settled  water. 
Under  conditions  of  over-treatment  with  lime,  calcium  carbonate 
will  precipitate  on  the  sand  grains,  causing  them  to  grow  in  size 
until  they  become  ineffective  for  filtering  purposes.  Dirty  sand 
can  be  removed,  washed,  and  replaced;  sand  coated  with  lime  must 
be  replaced  with  new.  Hard  washing  will  remove  a  proportion  of 
the  finer  particles  of  sand,  and  it  is  advisable  to  keep  on  hand  a 
supply  of  finer  sand  and  replenish  the  filters  by  spreading  a  thin 
layer  of  this  over  the  coarser  sand.  Clogged-up  strainers  can  be 
cleaned  by  immersing  in  dilute  hydrochloric  acid  until  the  deposit 
is  dissolved  and  then  washing  to  remove  the  surplus  acid. 

When  a  filter  is  operating,  silt  and  coagulum  are  continually 
collecting  in  the  upper  part  of  the  sand,  causing  an  increasing  re- 
sistance to  the  passage  of  water,  until  a  point  is  reached  at  which 
the  pressure  of  water  above  the  sand  is  not  sufficient  to  force  the 
rated  quantity  through  the  filter.  A  vacuum  is  then  formed 
below  the  sand  surface,  as  the  water  is  running  through  the  lower 
part  of  the  sand  faster  than  it  can  pass  through  the  clogged  upper 
portion  under  the  water-head  alone,  and  this  vacuum  aids  in  keep- 
ing the  filter  up  to  its  capacity.  This  decrease  in  pressure  causes 
dissolved  gases  to  come  out  of  solution  and  collect  at  the  point 
of  maximum  vacuum,  forming  a  film  of  gas  across  the  filter  which 
effectually  stops  the  passage'  of  water.  This  gas  is  partly  air  and 
partly  carbonic  acid,  and  is  further  augmented  by  air  drawn  into 
the  filter  through  defective  flanges  and  valve  stems  in  the  effluent 
pipe.  If  the  effluent  pipe  is  closed,  the  air  will  rise  to  the  surface 
in  large  bubbles,  breaking  up  the  mat  and  forming  passages 
through  the  sand.  The  filter  must  then  be  washed  before  again 
being  placed  in  service. 

There  is  a  tendency  for  scum  and  foam  to  collect  on  the  walls 
of  the  filters  near  the  water-line  and  on  the  wash-water  troughs. 
This  is  unsightly,  and  should  be  cleaned  off  frequently. 

Washing  Filters.  The  method  of  washing  filters  depends  on 
the  design  of  the  filter,  which  may  be  one  of  three  types:  the  old 
circular  tank  type,  provided  with  revolving  rakes  for  agitation; 


202  WATER    PURIFICATION    PLANTS 

the  concrete  unit  provided  with  air  agitation;  or  the  most  recent 
"  hard-wash  "  type. 

a.  Revolving-rake  type : 

1.  Close  influent  valve  and  allow  water  to  draw  down  to  top 
of  troughs. 

2.  Close  effluent  valve. 

3.  Open  sewer  full  wide. 

4.  Open  wash- water  valve  very  slowly. 

5.  While  wash  water  is  rising,  allow  agitating  rakes  to  trail 
backward  slowly. 

6.  Start  agitating  rakes  forward  at  10  to  12  revolutions  per 
minute. 

7.  When  filter  is  sufficiently  washed,  start  agitator  trailing 
backward  and  slowly  close  wash- water  valve. 

8.  Close  sewer  valve. 

9.  Open  influent  valve  and  allow  water  to  come  to  normal 
level. 

10.  Open  effluent  valve  slightly  and  after  about  five  minutes 
open  fully. 

b.  Air-agitation  type : 

1.  Close   influent    valve   and  allow  water  to  draw  down  to 
top  of  troughs. 

2.  Close  effluent  valve. 

3.  Open  sewer  fully. 

4.  Open  air  valve — (keep  air  on  about  3  minutes). 

5.  Close  air  valve  and  open  wash  water  valve  slowly. 

6.  When  filter  is  sufficiently  washed,  slowly  close  wash-water 
valve. 

7.  Close  sewer  valve. 

8.  Open  influent  valve  and  allow  water  to  come  to  normal  level. 

9.  Open  effluent  valve  slightly  and  after  about  five  minutes 
fully. 

c.  Hard-wash  type : 

1.  Close  influent  valve  and  allow  water  to  draw  down  to  top 
of  troughs. 

2.  Close  effluent  valve. 

3.  Open  sewer  fully. 

4.  Open  wash-water  valve  slowly. 

5.  When  filter  is  sufficiently  washed,  close  wash-water  valve 
very  slowly. 


FILTRATION   AND    GENERAL   OPERATION  203 

6.  Close  sewer  valve. 

7.  Open  influent  valve  and  allow  water  to  come  to  normal 
level. 

8.  Open  effluent  valve  slightly  and  after  about  five  minutes 
fully. 

As  to  rate  of  wash,  this  should  be  as  high  as  possible  without 
washing  away  any  sand.  To  test  this,  wash  the  filter  thoroughly 
clean,  then  with  different  openings  of  the  wash  valve,  collect 
samples  of  water  from  the  wash  troughs  in  large  glass  jars.  Allow 
these  to  stand  and  note  whether  any  sand  settles  out.  The 
highest  rate  at  which  no  sand  appears  should  be  used,  and  can  be 
conveniently  gaged  by  the  number  of  turns  the  wash  valve  is 
open.  A  pressure  gage  attached  to  the  wash  pipe  as  it  enters  the 
filter  furnishes  a  convenient  method  of  measuring  the  rate  of 
wash. 

Washing  should  be  continued  until  all  the  heavy  dirt  is  removed , 
but  not  until  the  filter  is  perfectly  clean,  as  it  is  desirable  to  have 
a  film  of  coagulant  jelly  about  /(e  inch  thick  over  the  entire  sand 
surface  to  form  a  mat  when  starting  the  filter,  and  to  wash  beyond 
a  certain  stage  requires  an  excessive  amount  of  wash  water.  The 
total  time  for  washing  is  generally  about  8  to  12  minutes  per  filter. 

An  inspection  of  the  sand  surface  after  washing  forms  a  good 
criterion  of  the  rate,  length,  and  distribution  of  wash.  The  sur- 
face should  be  covered  with  a  uniform  film  of  jelly  as  above 
mentioned.  Removing  this,  the  sand  should  be  absolutely  clean. 
The  presence  of  mud  uniformly  distributed  would  indicate  too 
short  a  period  of  washing  or  too  low  a  rate.  Mud  near  the  sides 
of  the  wash  troughs  denotes  that  these  are  too  far  apart  and  can  be 
partially  remedied  by  a  higher  rate  and  longer  period.  Isolated 
mud  patches  suggest  stopped-up  strainers,  especially  if  the  sand 
beneath  is  not  clean.  Craters  of  sand  are  signs  of  water  channels 
due  to  vertical  stratification,  broken  strainers,  or  air  pipes.  Mud- 
balls  occur  with  low  rates  of  wash.  These  and  other  accumula- 
tions of  mud  should  be  carefully  removed  with  a  long-handled 
spade. 

It  is  important  that  the  wash  valve  be  opened  and  especially 
closed  very  slowly.  This  has  the  effect  of  leaving  the  sand 
stratified  horizontally  in  layers  of  increasing  fineness  upward,  and 
therefore  in  the  best  condition  for  filtering. 

It  is  not  best  to  wash  all  the  filters  in  succession,  but  this 


204  WATER   PURIFICATION   PLANTS 

work  should  be  divided  proportionately  among  the  shifts,  as  this 
tends  toward  greater  uniformity  of  the  effluent  and  causes  less 
unbalancing  of  operating  conditions.  In  small  plants,  say  of  three 
units,  washing  one  filter  throws  50  per  cent  more  water  into  each 
of  the  others,  which  may  disturb  their  operation,  especially  with 
a  small  settling  basin  or  poorly  regulating  controllers. 

Clear- Water  Basin.  The  clear-water  basin  should  be  kept 
scrupulously  clean.  Hatchways  leading  into  it  should  be  tightly 
covered;  and  if  necessary  to  enter  it  while  in  use,  great  care  should 
be  used  to  prevent  its  pollution  in  any  way.  If  the  pipe  gallery  is 
of  the  open  type,  i.e.,  used  as  or  connected  with  the  clear-water 
basin,  the  raw-water  and  sewer  pipes  should  be  inspected  at  least 
weekly  for  leaks.  The  same  holds  for  the  fronts'  of  the  filter 
tubs,  if  forming  part  of  the  walls  of  the  clear- water  basin. 

Laboratory.  It  would  seem  almost  needless  to  say  that  all 
apparatus,  reagents,  etc.,  must  be  kept  perfectly  clean,  and  that 
all  tests  must  be  made  with  scrupulous  care,  yet  in  these  particulars 
the  grossest  negligence  is  often  found,  especially  in  small  plants. 
The  room  and  furniture  should  be  kept  free  from  dust  to  prevent 
pollution  of  bacterial  tests.  Reagents  should  not  be  allowed  to 
grow  stale  and  must  be  standardized  frequently  to  insure  their 
correctness.  This  applies  as  well  to  distilled  water,  which  often 
contains  traces  of  impurities.  A  good  way  to  test  reagents  is  to 
run  blank  analyses  with  distilled  water  of  known  purity  and 
record  the  results.  The  stoppers  of  reagent  bottles  should  never 
be  laid  upon  the  desk,  unless  upon  a  clean  paper,  and  the  neck 
and  mouth  of  such  bottles  should  be  kept  scrupulously  clean,  and 
the  mixing  up  stoppers  avoided.  The  reagent  should  be  added 
very  slowly  with  constant  stirring.  Glassware,  except  for  bac- 
terial tests,  should  always  be  wiped  with  a  clean  lintless  towel  just 
before  use.  The  work  should  be  laid  out  so  as  to  secure  the 
best  economy  of  time.  Thus  if  one  test  involves  a  lengthy  filtra- 
tion or  boiling  of  the  sample,  another  test  can  be  run  while  this  is 
in  progress.  A  note-book  should  be  kept  containing  a  dated 
record  of  all  tests  and  computations  systematically  and  neatly 
arranged. 

Calibration  of  Apparatus.  In  order  to  adjust  the  chemical 
dosage  properly,  it  is  necessary  that  the  means  of  measuring  the 
raw- water  pumpage  be  accurate.  Whether  this  be  determined  by 
Venturi  meter,  weirs,  stroke  counter,  or  tachometer,  the  accuracy 


FILTRATION  AND   GENERAL   OPERATION  205 

of  the  device  should  be  tested.  If  a  stroke  counter  or  tachometer 
is  used,  the  test  should  be  repeated  at  intervals,  as  the  slippage 
factor  of  the  pumps  changes  from  time  to  time.  This  test  is  best 
made  by  closing  the  outlet  of  the  settling  basin  into  which  the 
pumps  deliver,  and  measuring  the  rise  in  water  in  the  basin  and 
the  number  of  revolutions  made  by  the  pumps  discharging  into  the 
basin,  in  a  given  time.  Then  from  the  area  of  the  basin  and 
the  rise  in  water  level,  the  pumpage  can  be  calculated  in 
cubic  feet,  and  this  quantity  multiplied  by  7.5  and  divided 
by  the  number  of  revolutions  gives  the  gallons  pumped  per 
revolution. 

Example.  A  reciprocating  pump  being  tested  delivers  into  a 
basin  40  X  80  feet  in  plan.  The  duration  of  the  test  is  30  minutes, 
the  rise  in  the  basin  is  1.83  feet,  the  number  of  revolutions  made 
by  the  pump  is  943^. 

Area  of  basin  =      40  X  80      =    3,200  sq.  ft. 

Volume  pumped  =  3200  X  1.83    =    5,850  cu.  ft. 

Gallons  pumped  =  5850  X  7.5     =  43,875  gallons 

Gallons  per  revolution  =  43875  -5-  943J  =  46.502  gal.  rev. 

In  testing  centrifugal  pumps,  the  rise  should  be  one  foot  or  less, 
the  water  level  in  starting  being  six  inches  below  that  normally 
carried  in  the  basin,  and,  on  stopping,  six  inches  above  normal  level. 
Centrifugal  pumps  should  be  tested  at  various  speeds  and  a  curve 
showing  the  relation  between  speed  and  capacity  should  be  plotted. 

Venturi  meters  are  tested  in  a  similar  manner,  the  computed 
discharge  in  gallons  being  compared  with  the  registered  discharge 
of  the  meter,  the  latter  being  corrected  if  a  discrepancy  develops. 

The  rate  of  filtration  can  be  checked  in  a  similar  manner,  by 
closing  the  influent  valve  and  measuring  the  drop  in  water  level 
for  one  minute.  The  area  of  the  filter  in  square  feet  multiplied  by 
0.625  times  the  drop  in  inches  gives  the  rate  of  filtration  in  gallons 
per  minute.  By  repeating  this  test  with  different  losses  of  head 
through  the  filter,  the  adjustment  of  the  rate  controllers  can  be 
checked. 

By  a  similar  process  the  rate  of  washing  can  be  obtained. 

The  solution  tanks  and  orifice  boxes  should  be  calibrated.  This 
is  done  by  first  measuring  the  cubical  contents  of  the  tanks,  and 
multiplying  this  by  7.5  to  obtain  the  capacity  in  gallons.  Then, 


206  WATER   PURIFICATION   PLANTS 

with  the  orifice  open  to  a  certain  mark,  note  how  far  the  water 
level  in  the  solution  tank  drops  in  a  given  time.  From  this  the 
rating  of  the  orifice  can  be  obtained.  The  test  should  be  repeated 
for  different  orifice  openings  and  a  table  or  curve  plotted  giving 
the  rate  of  discharge  of  the  orifice  for  different  openings. 

Besides  making  the  above  tests,  the  operator  should  measure 
and  compute  the  capacities  of  all  the  various  units  in  the  plant, 
and  make  a  permanent  record  of  the  results  for  reference.  This 
should  include  the  ratings  of  all  pumps,  capacities  of  settling 
basins,  filters,  clear-water  basins,  wash-water  tank,  solution 
tanks,  etc. 

Organization.  The  organization  of  the  force  operating  a 
filtration  plant  depends  principally  on  the  size  of  the  plant,  to  a 
less  extent  on  whether  or  not  softening  is  attempted.  Small 
plants  connected  with  public  institutions  or  supplying  villages 
require  only  a  portion  of  one  man's  time,  who  may  also  act  as 
pumping-station  engineer  or  perform  other  duties.  Plants  in 
small  towns,  which  operate  only  part  of  each  day,  can  be  managed 
by  one  man,  with  possibly  the  occasional  help  of  several  laborers 
for  cleaning  and  repairs.  The  same  plant,  so  situated  that,  be- 
cause of  lack  of  storage  facilities,  it  must  be  run  continuously, 
twenty-four  hours  per  day,  must  obviously  have  at  least  one 
man  per  shift. 

In  towns  and  cities  of  moderate  size,  say  20,000  to  60,000  in- 
habitants, the  force  would  generally  consist  of  a  chemist,  assistant 
chemist,  three  filter  operators,  three  coagulant  house  operators, 
and  a  janitor  and  utility  man,  in  all  nine  men.  The  chemist 
would  have  general  supervision  of  the  plant,  besides  making  the 
chemical  and  bacteriological  determinations.  The  assistant 
chemist  would  assist  in  the  laboratory  work  and  in  keeping  the 
records,  and  would  make  the  necessary  tests  in  the  absence  of  the 
chemist.  The  duties  of  the  filter  men  and  the  coagulant  house 
operators  are  obvious,  there  being  one  each  of  these  per  shift.  In 
smaller  plants  the  two  positions  can  be  combined,  thereby  eliminat- 
ing three  men.  The  utility  man  will  do  janitorial  work  most  of  the 
time,  but  should  be  ready  to  assist  wherever  required  or  to  replace 
any  of  the  operators  in  emergency. 

In  plants  of  large  size,  there  is  not  only  a  corresponding  in- 
crease in  personnel,  but,  owing  to  the  complex  apparatus  used, 
skilled  workmen  are  required.  A  superintendent  is  necessary, 


FILTRATION   AND    GENERAL    OPERATION 


207 


who  has  entire  charge  of  the  plant.  There  should  be  at  least  one 
chemist  and  one  bacteriologist,  either  being  capable  of  taking  over 
the  other's  work.  In  the  absence  of  the  superintendent,  the 
plant  should  be  in  charge  of  the  chemist.  There  would  probably 


Assistant 


Bacteriologist 


o 


9C  cr  Q    o 

A     \0peratbrs 


o  O\Q\ 


Laborers     V, 
Coagulant  House  \    \    \ 


<xX  o 


Laborer 
Filter  House 


tf  o 


Utility  Men 
FIG.  89. — Organization  Chart  for  a  Large  Filtration  Plant. 

be  one  foreman  and  one  laborer  in  the  coagulant  house,  and  one 
filter  operator,  in  each  shift.  There  should  be  at  least  one  skilled 
mechanic  and  electrician,  and  a  foreman  with  several  laborers  to 
look  after  any  outside  or  repair  work,  such  as  cleaning  basins,  re- 
placing filter  sand,  etc.  A  janitor,  utility  man,  and  a  clerk  will  also 


208  WATER   PURIFICATION   PLANTS 

be  required.  Such  an  organization  is  shown  by  the  chart, 
Fig.  89. 

Cost  of  Operation.  Perhaps  the  largest  single  factor  affecting 
the  cost  of  operation  of  filtration  plants  is  the  amount  of  coagulant 
used.  This  varies  with  the  quality  of  the  raw  water,  and  in- 
creases greatly  when  the  water  is  softened.  The  labor  cost  in- 
creases with  the  size  of  plant  from  the  smallest  to  plants  of  perhaps 
10,000,000  gallons  capacity,  after  which  the  cost  per  million 
gallons  decreases.  Against  the  cost  of  filtering  should  be  charged 
the  cost  of  pumping  the  water  against  the  head  lost  in  filtration, 
which  is  generally  from  10  to  15  feet.  The  following  are  typical 
examples  of  the  cost  of  filtration  in  plants  of  various  sizes : 

Example  No.  1.  Cost  of  Coagulation  and  Sedimentation  at 
St.  Louis,  Mo.  The  treatment  consists  of  coagulation  with  lime 
and  iron  sulphate,  followed  by  sedimentation  in  large  basins. 
The  source  of  supply  is  the  Mississippi  River  below  the  mouth  of 
the  Missouri,  consequently  a  very  high  turbidity  prevails  much  of 
the  time.  The  average  amounts  of  chemicals  used  in  1911  were 
5.77  grains  per  gallon  of  lime  and  2.70  grains  per  gallon  of  iron 
sulphate. 

Cost  of  Purification  per  Million  Gallons  (1910-1911) 

Lime $1.967 

Sulphate  of  iron 1.969 

Unloading 0.094 

Operating  amd  maintenance  (labor) 0 . 378 

Repairs 0.030 

Water,  coal,  oil,  etc 0.047 

Light  and  power 0 . 098 

Water  analyses  (chemist's) 0. 172 

Total ..$4.755 

The  average  daily  pumpage  was  about  86,000,000  gallons. 

Example  No.  2.    Cost  of  Filtration  at  Harrisburg,   Penna. 

This  is  a  standard  type  mechanical  filtration  plant.  The  pumpage 
for  1911  averaged  8,205,684  gallons  per  day.  The  average  amount 
of  coagulant  used  was  0.7  grain  per  gallon. 


FILTRATION    AND    GENERAL    OPERATION  209 

Cost  of  Purification  per  Million  Gallons  (1910-1911) 

Coagulant $1 . 22 

Fuel  (low  service) 0 . 86 

Supplies 0. 28 

Materials  and  repairs 0 . 36 

Oil  and  waste 0. 07 

Laboratory 0 . 43 

Labor. .  .2.77 


Total $5.99 

Example  No.  3.    Cost  of  Filtration  at  a  Typical  Small  Plant. 

Daily  pumpage,  2,000,000  -gallons.  Water  slightly  acid  at  times, 
requiring  the  use  of  soda  ash.  Average  amounts  of  coagulant 
used  0.7  grain  per  gallon  of  alum,  0.5  grain  per  gallon  of  soda  ash. 

Cost  of  Purification  per  Million  Gallons 

Alum $1.25 

Soda  ash 86 

Fuel  (low  service)* 73 

Supplies,  oil,  and  waste 42 

Repairs 07 

Labor..  .   2.00 


Total $5.33 

Example  No.  4.  Cost  of  Purification  in  a  Large  Softening 
Plant.  Daily  pumpage,  50,000,000  gallons;  lime  used,  8  grains  per 
gallon;  iron  sulphate,  1  grain  per  gallon.  Plant  is  equipped  with 
conveyers,  automatic  scales,  and  other  labor-saving  devices. 

Cost  of  Purification  per  Million  Gallons 

Lime $2.71 

Iron  sulphate 0. 72 

Labor 0.69 

Material,  supplies,  and  repairs 0.56 

Laboratory 0.12 

Low-service  pumpage  * 0 . 40 


$5.20 


Cost  of  pumping  the  additional  head  lost  in  the  filtration  plant. 


210  WATER   PURIFICATION    PLANTS 

BARKER VILLE  FILTER  PLANT 
DAILY  REPORT 

Date 

Weather 

Hours  pumped Amount  pumped Gallons 

Alum  used Pounds Gr/Gal. 

Lime  used Pounds Gr/Gal. 

Filters  washed Time Minutes 

Wash  water  used Gallons %  of  raw 

Analyses :                                 Raw  water                  Filtered  water 
Turbidity ... 


Color 

Alkalinity 

C02 

Bacteria 

Coli.. 


Remarks: 


Signed 

Operator 

FIG. — 90.    Daily  Report  Form  for  a  Small  Purification  Plant. 


FILTRATION   AND   GENERAL   OPERATION  211 

Records  and  Statistics.  The  records  to  be  kept  depend 
largely  upon  the  size  and  purpose  of  the  plant.  Even  in  the  small- 
est plants  a  note-book  should  be  kept  in  which  results  of  analyses, 
amounts  of  water  pumped,  and  chemicals  used  should  be  recorded. 
In  any  but  institutional  plants,  a  daily  form  similar  to  Fig.  90 
should  be  filled  out,  preferably  in  duplicate,  one  copy  being  sent 
to  the  water-works  office  for  record  and  the  other  being  kept  on 
file  at  the  plant.  It  is  convenient  to  keep  these  reports  on  paper 
of  some  standard  loose-leaf  system.  The  operator  should  also 
keep  an  accurate  record  of  the  time  of  men  employed  about  the 
plant,  material  received,  and  such  events  as  cleaning  the  basins, 
renewing  filter  sand,  and  the  like. 

In  large  plants,  especially  if  municipally  owned,  more  complete 
records  must  be  kept.  These  should  include: 

a.  Laboratory  note-books. 

b.  Diary. 

c.  Time  and  material-book. 

d.  Plant  invoice  and  data. 

e.  Daily  report. 
/.  Annual  report. 

The  laboratory  note-books  should  contain  complete  data, 
computations,  and  results  of  all  tests  made  in  the  laboratory. 
These  are  best  kept  in  chronological  order  in  books  of  uniform  size 
and  appearance.  It  may  be  well  to  have  separate  books  for 
physical  and  chemical  water  analyses,  bacteriological  analyses, 
analyses  of  coagulants,  etc.,  to  prevent  interference  if  several  of 
these  are  conducted  at  once,  and  to  render  the  records  more 
accessible. 

The  diary  is  best  kept  by  the  superintendent  himself,  and 
should  contain  events  of  importance  in  sufficient  detail  to  make  it 
a  running  history  of  the  plant. 

The  time-  and  material-book  should  contain  the  time  of  all 
employees  and  a  record  of  all  material  received.  This  would  con- 
tain entries  of  the  amounts  and  quality  of  coagulants  received, 
laboratory  supplies,  packing,  oil,  light,  and  steam  used,  etc. 

A  book  should  be  kept  giving  a  list  of  apparatus  in  the  plant, 
capacities  of  basins,  filters,  clear  well,  ratings  of  controllers,  orifices, 
etc.,  for  ready  reference. 

A  short  form  of  daily  report  has  already  been  given.     Fig.  91 


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FILTRATION   AND    GENERAL    OPERATION  213 

gives  a  more  elaborate  form  for  use  in  a  large  plant.  This  is 
arranged  to  take  care  of  a  week's  data.  It  should  be  made  out 
in  duplicate,  and  with  the  copy  sent  to  the  head  office  should  be 
included  a  list  of  materials  and  supplies  used,  and  a  short  account 
of  the  week's  occurrences  at  the  plant. 

The  annual  report  should  contain  a  summary  of  the  year's 
work.  This  should  include  average  daily  and  total  pumpages, 
monthly  average  turbidity,  bacterial  count,  alkalinity,  etc.,  in  the 
raw,  settled,  and  filtered  water;  amounts  of  coagulants  used  as 
minimum,  average,  and  maximum  monthly  values  in  grains  per 
gallon,  and  as  the  total  amounts  consumed,  percentage  of  wash 
water  used,  and  other  pertinent  data.  It  should  also  contain  a 
summarized  statement  of  all  expenditures,  and  the  itemized  cost 
of  filtration  per  million  gallons.  The  history  of  the  plant  for  the 
last  year  should  be  briefly  given,  and  the  policy  for  the  coming 
year  briefly  outlined.  In  connection  with  the  annual  report,  at- 
tention is  called  to  the  form  evolved  by  the  committee  on  filter 
operation  of  the  New  England  Waterworks  Association. 

To  care  for  the  letters,  bills,  invoices,  etc.,  received  in  con- 
nection with  the  operation  of  the  plant,  a*  filing  system  of  the  usual 
type,  should  be  installed,  and  there  should  be  the  usual  account- 
books  in  which  to  enter  financial  transactions. 

Automatic  Records.  Automatic  recording  devices  are  com- 
ing into  vogue  in  filtration  plants.  These  record  graphically, 
on  charts,  the  indications  of  meters  and  gages,  and  furnish  a  con- 
tinuous record  of  their  operation.  They  are  generally  attached  to 
the  apparatus  and  furnish  the  data  given  in  the  following  list : 

Automatic  Recorders 

Apparatus  Whereto  Attached  Data  Recorded 

a.  Raw-water  Venturi  meter  Raw  water  treated 

6.  Wash- water  Venturi  meter  Wash  water  used 

c.  Wash-water  main  Wash-water  pressure 

d.  Loss-of-head  gages  Loss  of  head  in  each  filter 

e.  Effluent  controllers  Rate  of  filtration  per  filter 
/.   Clear-well  gage  Depth  of  water  in  clear  well 
g.  Coagulant  solution  tanks  Amount  of  solution  used 

h.    Coagulant  scales  Amount  of  coagulant  used 

While  all  of  these  records  have  a  certain  value,  the  use  of  these 
devices  involves  considerable  care,  and  the  accumulation  of  charts 


214  WATER    PURIFICATION    PLANTS 

soon  becomes  overwhelming.  However,  a  limited  number  of 
automatic  recorders  are  of  much  value.  This  is  particularly  true 
of  the  raw-water  and  wash-water  meters.  An  automatic  record 
of  the  amounts  of  coagulant  used  would  be  very  useful  in  correcting 
irregularities  of  feeding  same.  This  is  quite  readily  accomplished 
with  the  various  methods  of  dry  feeding  described,  or  with  auto- 
matic scales,  by  having  an  electric  contact  close  at  each  revolution 
of  the  device  (or  every  time  the  scale  discharges),  and,  by  actuating 
a  solenoid,  cause  a  mark  to  be  made  on  a  clock-driven  chart.  It 
is  less  easily  done  where  adjustments  are  made  both  in  the  strength 
and  amount  of  solution  fed  to  the  water.  Continuous  records  of 
loss  of  head,  rate  of  filtration,  etc.,  hardly  seem  necessary  in  a  well- 
regulated  plant. 

Electric  Alarms  and  Intercommunication.  In  all  filtration 
plants  there  is  need  for  certain  electric  or  automatic  alarms.  In 
the  small  plant  it  is  highly  desirable  that  a  device  be  installed  to 
actuate  an  alarm  in  the  filter  building  whenever  the  water  level 
in  the  settling  basins  reaches  the  point  of  overflow,  as  their  over- 
flowing results  in  a  waste  of  water  and  coagulant.  This  is  simply 
arranged  by  means  of  a  float  in  the  settling  basins  which  will  close 
a  circuit  and  ring  a  bell  in  the  filter  building  when  the  water 
reaches  a  predetermined  height.  If  the  pumping  station  is 
separated  from  the  filter  plant,  a  second  bell,  in  series  with  the 
first,  should  be  placed  there,  so  that  the  engineer  may  reduce  the 
speed  of  the  pumps  if  the  basins  threaten  to  overflow.  Similar 
alarms  should  be  placed  on  the  clear  well  and  the  solution  tanks, 
the  latter  indicating  when  these  have  run  down,  so  that  they 
may  be  replenished  before  becoming  entirely  empty. 

In  large  plants  there  should  be  a  system  of  intercommunicating 
telephones  between  the  superintendent's  office,  laboratory,  filter 
building,  coagulant  house,  and  pumping  station.  If  the  coagulant 
house  is  at  some  distance  from  the  superintendent's  office,  it  may 
be  advisable  to  have  instruments  installed  which  will  indicate  the 
operation  of  the  orifice  boxes  and  other  coagulant  devices  therein. 
Of  course,  the  alarms  on  the  settling  basins  and  clear  well  are  even 
more  desirable  in  a  large  plant  than  in  a  small  one,  as  the  wastage 
due  to  overflowing  is  correspondingly  greater. 

The  Construction  and  Interpretation  of  Graphical  Charts. 
In  filter-plant  operation  and  records,  graphical  charts  of  a  simple 
type  can  sometimes  be  usefully  employed.  This  is  particularly 


FILTRATION   AND    GENERAL    OPERATION 


215 


true  when  it  is  desired  to  record  data  wherein  two  variable  quanti- 
ties are  dependent  upon  each  other,  as,  for  instance,  the  variation 
in  the  turbidity  or  other  quality  of  the  water  from  day  to  day; 
the  variation  in  discharge  of  a  pump  at  different  speeds. 

The  paper  on  which  such  charts  are  constructed  is  ruled  with 
horizontal  and  vertical  lines,  evenly  spaced.  These  lines  are 
generally  arranged  in  multiples  of  ten,  every  tenth  line  being 
heavier  than  the  rest,  and  sometimes  every  fifth  line  is  also  made 
slightly  heavier  for  ease  in  reading.  Such  paper  is  obtainable, 
ruled  ready  for  use,  at  any  scientific  supply-house. 

As  an  example  of  the  use  of  this  so-called  " coordinate"  paper, 
let  us  suppose  that  a  calibration  test  has  been  run  on  a  centrifugal 


1430 


1430 


UQO 


13J8 


1330 


Re 


utions 


Minute 


FIG.  92. 

pump,  discharging  against  a  constant  head,  in  order  to  determine 

the  discharge  in  gallons  per  minute  for  different  speeds.     The 
data  obtained  may  be  as  follows: 

Speed  (in  rev.  per  minute)  Discharge  (in  gal.  per  minute) 

a.  315  1,256 

b.  329  1,312 

c.  350  1,398 

d.  366  1,460 

e.  374  1,495 


216  WATER    PURIFICATION    PLANTS 

Taking  a  piece  of  coordinate  paper,  Fig.  92,  a  scale  of  speeds  is 
laid  out  horizontally  along  the  lower  margin.  We  will  call  one 
of  the  left-hand  vertical  lines  300  (revolutions  per  minute), 
and  assuming  each  space  between  verticals  to  correspond  to  an 
increase  of  two  revolutions  per  minute,  the  next  heavy  vertical 
line,  ten  spaces  above  the  first,  would  be  marked  320  revolutions 
per  minute,  the  following  one  340,  etc.  In  the  same  way  a  scale 
of  discharge  capacity  is  laid  off  along  the  left  margin,  each  space 
between  two  horizontal  lines  corresponding  to  an  increase  in  dis- 
charge of  ten  gallons  per  minute.  Thus  starting  with  a  discharge 
of  1,300  (gallons  per  minute),  at  a  heavy  line  near  the  bottom 
of  the  sheet,  the  next  heavy  line  would  be  1,350,  the  next  1,400,  etc. 
We  are  now  ready  to  plot  the  corresponding  values  determined 
in  the  test.  Taking  the  values  (a) ,  draw  a  light  pencil  line  through 
the  vertical  corresponding  to  315  on  the  sheet,  and  another 
similar  line  through  the  horizontal  corresponding  to  1,256.  Where 
the  two  lines  intersect  make  a  dot,  which  gives  the  point  on  the 
chart  representing  the  values  for  speed  and  discharge  for  the  two 
corresponding  determinations  (a).  In  a  similar  manner  find 
points  for  (b),  (c),  (cf),  and  (e).  A  line  drawn  through  these  points 
gives  the  relation  between  speeds  and  discharge  for  the  centrifugal 
pump,  and  has  the  advantage  over  the  tabulated  data  that  in- 
termediate values,  not  determined  by  test,  can  be  read  off  directly 
from  the  line  or  "  curve  "  on  the  chart.  The  line  thus  determined 
is  not  always  straight,  but  may  be  a  curve  taking  a  variety  of 
forms.  Sometimes,  too,  the  points  determined  do  not  lie  on  any 
connected  line  or  curve,  which  results  from  inaccuracies  of  the  test. 
In  such  cases  a  "  curve  "  is  generally  drawn  approaching  the 
points  as  closely  as  possible. 

As  another  example,  let  it  be  desired  to  plot  graphically  the 
turbidity  of  a  water  for  successive  days.  Let  the  data  be  as 
follows : 

Date  Turbidity  (in  parts  per  million') 

Jan.  1,  1915 75 

Jan.  2,  1915 90 

Jan.  3,  1915 116 

Jan.  4,  1915 60 

Jan.  5,  1915 88 

Along  the  lower  margin  of  a  sheet  of  coordinate  paper,  Fig.  93,  lay 


FILTRATION   AND    GENERAL   OPERATION 


217 


off  the  time  in  days,  allowing  one  space  for  each  day.  Vertically 
along  the  left-hand  margin  lay  off  a  scale  for  turbidities,  allowing 
each  space  between  horizontal  lines  to  equal  five  parts  per  million. 
Then  plot  the  turbidities  and  corresponding  dates,  as  was  done  in 
the  first  case.  . 

A  daily  graphical  record  of  all  the  tests  made  at  the  plant,  while 
troublesome  to  make,  is  very  instructive  and  presents  the  data 
in  much  more  comprehensible  form  than  any  number  of  report 
sheets  or  monthly  averages.  A  portion 
of  such  a  record  is  shown  in  Fig.  94. 

Economy  in  Operation.  It  is  of 
course  incumbent  upon  the  operator 
to  conduct  the  plant  as  economically 
as  possible.  Efforts  toward  this 
end  should  be  made  in  the  following 
directions : 

a.  Careful  adjustment  of  amounts 
of  coagulants  to  the  needs  of  the 
water. 

6.  Elimination  of  wastes  in  hand- 
ling coagulants. 

c.  Prevention  of  overflow  and  leak- 
age of  water. 

d.  Regulation  of  wash  water   to 
the  requirements. 

e.  Reduction    of    loss    of     head 
through  plant  to  a  minimum. 

/.  Profitable  employment  of  labor. 

g.  Avoidance  of  waste  in  mate- 
rials and  supplies. 

The    problem   of    adjustment  of 

coagulants  to  the  conditions  of  the  water  so  as  to  obtain  most  eco- 
nomical results  is  best  attacked  along  the  following  line :  A  suffi- 
cient length  of  time  after  making  the  tests  and  determining 
upon  the  amount  of  coagulant  to  allow  the  effect  to  become 
noticeable  in  the  basins,  a  careful  inspection  is  made  of  the 
coagulation  and  the  amount  of  coagulant  is  readjusted 
in  accordance  with  the  rules  already  formulated.  A  sheet 
of  coordinate  paper  is  then  arranged,  similar  to  Plate  III, 
with  a  turbidity  scale  along  the  left-hand  margin,  and  a  scale  for 


no 

100 
90 

so 

TO 
60 
50 
40 
80 
80 
10 

Jan  11  a 

1 

I 

3 

4 

5 

6 

7 

8 

9 

10 

11 

— 

FIG.  93. 


218 


WATER    PURIFICATION    PLANTS 


coagulant  in  grains  per  gallon  along  the  lower  margin.     On  this 
a  point  is  plotted  each  day,  its  position  being  determined  by  the 


August 


100 
90 
80 
70 
GO 
50 
40 
30 
20 
10 
0 


Septemb 


COAGULANTS  USED 
Grains  per  Gallon 


ANALYSIS 
Parts  per  Million 


FlG.  94. 


.Lime  ( Available  CaO) 


Iron  Sulphate (Pe  SOJ  H2O) 


Alkalinity  of  Raw  Water 


Water 
Overtreated 


Water 
Undertrcated 


Alkalinity  of  Filtered  Water 

Alkalinity  of  Filtered  Water 
with  Phenolphthalein  X  2 


Turbidity  of  Raw  Water 
<  Turbidity  of  Filtered  Water 


value  of  the  turbidity  of  the  water  and  the  grains  of  coagulant 
used.     After  a  period  of  six  months  there  will  be  some  180  dots 


FILTRATION   AND    GENERAL    OPERATION  219 

on  the  sheet.  For  a  given  turbidity,  there  may  be  several  dots, 
owing  to  the  fact  that  different  amounts  of  coagulant  were  used 
at  different  times.  Presumably,  under  similar  conditions,  the 
dot  representing  the  minimum  amount  of  coagulant  for  this 
turbidity  could  have  been  used  for  the  other  cases  where  a  similar 
turbidity  occurred,  and  this  point  can  be  marked  heavily.  Pro- 
ceeding similarly  for  other  turbidities,  a  series  of  heavy  dots  is 
obtained  through  which  a  curve  can  be  drawn,  giving  a  turbidity- 
coagulant  relation  for  future  use,  subject,  of  course  to  correction  as 
more  data  are  obtained.  The  economy  in  shifting  the  point  of 
application  of  the  coagulant  with  turbid  water  has  already  been 
considered. 

The  elimination  of  waste  in  the  coagulant  involves  buying 
this  on  specifications  based  on  its  chemical  purity  and  checking 
each  shipment  by  an  analysis.  The  shipments  received  should 
always  be  checked  as  to  weight.  The  care  required  in  handling 
and  preparing  solutions  of  lime  and  other  coagulants  has  already 
been  considered. 

There  is  often  considerable  wastage  of  coagulated  and  filtered 
water  in  a  filtration  plant.  That  due  to  overflowing  of  the  settling 
basins  can  be  largely  prevented  by  a  system  of  electric  alarms, 
as  already  described.  There  frequently  occurs  a  pronounced 
leakage  due  to  partially  closed  drain  valves  in  the  settling  basins 
and  clear  well,  the  remedy  for  which  is  obvious;  and  due  to  leaks 
in  the  walls  and  floors  of  these  structures.  Theoretically  the  raw 
water  pumped  should  equal  the  filtered  water  delivered,  barring 
slight  losses  in  washing  and  the  addition  of  coagulant  solutions. 
The  raw-water  pumpage  can  be  accurately  obtained  from  a  Venturi 
meter  or  closely  approximated  from  the  revolution  counters  of  the 
pumps.  As  modern  effluent  controllers  are  based  on  accurate 
hydraulic  principles,  the  amount  of  filtered  water  can  be  obtained 
from  the  rate  of  filtration  or  from  the  revolution  counters  of  the 
high-service  pumps.  If  the  wash -water  is  taken  directly  from  the 
clear  well  due  allowance  must  of  course  be  made.  If  the  amount 
of  water  filtered  is  appreciably  less  than  the  amount  of  raw 
water  pumped,  either  leakage  or  wasteful  operation  is 
indicated. 

The  amount  of  wash  water  and  rate  of  washing  should  be  regu- 
lated so  as  to  give  the  best  results.  Filters  need  be  washed  only 
when  the  loss  of  head  indicates  the  necessity  thereof,  unless  they 


220  WATER    PURIFICATION    PLANTS 

become  air-bound.  Often  the  amount  of  wash  water  used  is  in- 
creased above  that  required,  due  to  following  a  fixed  schedule  in 
washing,  regardless  of  the  condition  of  the  filter.  However,  the 
coating  and  clogging  of  the  sand  due  to  insufficient  washing  may 
ultimately  incur  a  greater  expense  in  its  removal  and  replacement 
than  the  cost  of  washing  somewhat  too  frequently. 

The  effect  of  properly  operating  coagulating  basins  in  reducing 
the  wash  water  required  has  already  been  mentioned. 

The  reduction  of  loss  of  head  through  the  plant  is  accomplished 
chiefly  by  keeping  the  clear  well  water  level  high.  This  reduces 
the  total  head  against  which  the  high-service  pumps  must  operate 
and  effects  a  reduction  in  fuel  cost. 

The  profitable  employment  of  labor  and  economy  in  materials 
and  supplies  must  be  left  to  the  executive  and  economic  ability 
of  the  man  in  charge  of  the  plant. 

General  Remarks.  The  attitude  of  the  public  toward  filtra- 
tion in  towns  where  a  plant  has  just  been  installed  is  often  one  of 
skepticism.  This  feeling  is  sometimes  augmented  through  de- 
rogatory statements  made  by  doctors  of  the  "  old  school,"  high- 
school  professors,  and  others  who  know  nothing  of  the  process,  but 
whose  utterances  carry  weight  because  of  their  supposed  scien- 
tific attainments.  For  purely  commercial  reasons,  venders  of 
bottled  mineral  waters,  etc.,  will  occasionally  badly  misquote 
filter  statistics.  The  best  way  to  overcome  this  tendency  is  to  keep 
the  plant  at  all  times  open  to  and  in  a  presentable  condition  for 
visitors,  and  to  induce  as  many  of  the  townspeople  as  possible  to 
come  and  see  it.  The  working  of  the  plant  should  be  explained  to 
visitors,  and  it  is  well  to  have  on  hand  diagrams  which  will  assist 
in  explaining  this  clearly.  In  some  large  plants  descriptive 
pamphlets  are  given  to  visitors. 

The  operator  should  feel  himself  under  moral  responsibility 
to  furnish  at  all  times  a  hygienically  safe  water,  this  duty 
transcending  all  others.  This  is  especially  true  because  any 
return  from  a  pure  to  an  impure  water,  even  for  a  short  time,  is 
almost  certain  to  be  followed  by  an  epidemic  of  intestinal  disease 
in  the  community,  regardless  of  the  fact  that  the  same  water  had 
been  used  with  immunity  for  years  before  filtration  was  started. 


Results  in  Parts  per  Million 
Graphical  Results  for  Tests  of  Alkalinity,  Acidity,  and  Carbonic  Acid. 


221 


PLATE  II. 


223 


PLATE  III. 


Hazen  Reciprocal  Turbidity 


Aluminum  Sulphate  (AL  (SO4)318  H2O)  Grains  per  Gallon 
Amounts  of  Aluminum  Sulphate  Required  for  Various  Turbidities. 


225 


PLATE  IV. 


UH 


227 


PLATE  V. 


snorref)  uomtK  J9cT  sntmo;r 


229 


PLATE  VI. 


Hazen  KeciprocafTurbidity 


Ferrous  Sulphate  (FESO4  7  H2O)  Grains  per  Gallon 
Amounts  of  Ferrous  Sulphate  Required  for  Various  Turbidities. 


231 


PLATE  VII. 


O  jad  sutmo  (os H  Z'OSIU)  adding  uoaj      »oo  eay;  p  t3 


233 


PLATE  VIII. 


I  ••••• SSSSS SSI! ••••*••••••••••• 


notniK  J3d  s^auj:  m  (snooao^)  uoaj 


235 


PLATE  IX. 


uon^o  aad  SUIBJQ  ut  pasn  ^uBinStJOQ 


237 


PLATE  X. 


239 


PLATE  XI. 


Gallons  of  Water  Required 


Ratio  of  Water  Required  to  Amount  of  Chemicals  Used  to  Make  Various 
Strengths  of  Solution  (Also  the  Daily  Discharge  of  Orifices  of  Various  Sizes). 


241 


APPENDIX  A 

ANALYSIS  OF  COAGULANTS 

Lime.  Determination  of  Per  Cent  Calcium  Oxid  (CaO). 
Weigh  out  0.28  gram  of  the  sample  on  an  accurate  balance. 
Place  in  an  Erlenmyer  flask  exactly  100  cc.  of  10  per  cent  cane- 
sugar  solution  made  with  cold,  freshly  boiled  distilled  water. 
Add  the  weighed  sample  of  lime  to  this  and  shake  until  no  further 
solution  is  taking  place.  Do  not  allow  any  lime  to  stick  to  the 
sides  of  the  flask.  Filter  through  a  dry  filter  and  titrate  50  cc. 
with  ^  sulphuric  acid  (H2S04),  with  phenolphthalein  indicator. 
The  amount  of  acid  solution  required  in  cc.  multiplied  by  2  gives 
the  per  cent  of  available  calcium  oxid.  As  prolonged  shaking  may 
be  required,  a  shaking  machine  is  desirable. 

Soda  Ash.  Dissolve  0.53  grams  of  the  sample  in  boiled 
distilled  water  and  make  up  to  100  cc.  Titrate  50  cc.  with  ^ 
sulphuric  acid  (H2SO4),  using  methyl  orange  as  an  indicator.  The 
number  of  cubic  centimeters  of  acid  required  multiplied  by  2  gives 
the  per  cent  of  water  soluble  soda  ash. 

Aluminum  Sulphate. 

a.  Total  Aluminum  Oxid  (AkOs).  Weigh  out  one  gram  of 
the  sample  and  dissolve  in  100  cc.  of  distilled  water.  Add  7  to  8  cc. 
of  ammonium  chlorid  (NH4C1),  heat 
to  boiling  and  precipitate  the  alumi- 
num as  hydroxid  by  adding  sufficient 
ammonium  hydroxid  (NH^OH)  to 
render  solution  slightly,  but  dis- 
tinctly alkaline.  Allow  solution  to 
stand  several  hours  at  near  boiling 
temperature  until  precipitate  has  all 
settled  out,  keeping  the  solution  al- 
kaline with  ammonium  hydroxid. 

Decant  the  clear  liquid    through    a  pIGi  95. Desiccator. 

filter,  wash    the   precipitate   several 

times  with  hot    water,    which    likewise  pour  through  the  filter, 
finally  bring  the  precipitate  on  the  filter  and  wash  several  times 

243 


244  WATER    PURIFICATION    PLANTS 

with  hot  water.  Place  filter  paper  and  contents  in  a  porcelain  or 
platinum  crucible,  heat  slowly  over  a  Bunsen  flame,  gradually 
increasing  the  heat,  and  finally  ignite  for  10  minutes  over  a  blast 
lamp.  Cool  the  crucible  in  a  desiccator  and  weigh.  An  ashless 
filter  paper  should  be  used  and  crucible  should  be  weighed  be- 
fore the  test.  The  weight  in  grams  times  100  gives  the  A1203  in 
per  cent. 

b.  Total  Sulphate  (as  SOS).  Weigh  out  1.0  gram  of  the  sample 
and  dissolve  in  200  cc.  of  distilled  water.  Acidify  with  con- 
centrated hydrochloric  acid  (HC1),  bring  to  boiling  and  pre- 
cipitate the  sulphate  with  a  slight  excess  of  barium  chlorid  (10 
per  cent),  added  slowly  with  constant  stirring.  Continue  boiling 
until  all  the  precipitate  has  settled  out  (about  10  minutes).  Allow 
the  solution  to  stand  and  cool  at  least  4  hours.  Decant,  filter,  and 
wash  as  under  a,  using  a  double  filter  paper.  Dry  and  ignite 
the  filter  paper  and  contents  in  a  weighed  crucible  over  a  Bunsen 
burner,  keeping  crucible  and  contents  at  dull  redness  for  10 
minutes.  Cool  and  weigh.  The  weight  in  grams  multiplied  by 
34.2  gives  the  per  cent  S03. 

Ferrous  Sulphate. 

a.  Total  Iron.    Dissolve  1.0  gram  of  the  sample  in  50  cc.  of 
distilled  water  and  immediately  add  15  cc.  of  concentrated  sul- 
phuric acid  (H2SO4).     Dilute  to  200  cc.  with  distilled  water  and 
titrate  with  potassium  permanganate  solution  (see  below),  until 
a  pink  color  appears.     The  number  of  cc.  permanganate  solution 
used  gives  the  percentage  of  iron  in  the  ferrous  sulphate. 

Permanganate  Solution.  Dissolve  6  grams  of  chemically  pure 
potassium  permanganate  in  a  little  less  than  a  liter  of  water. 
Weigh  out  exactly  0.7  gram  of  chemically  pure  ferrous  ammonium 
sulphate  and  place  it  in  a  beaker.  Add  50  cc.  of  distilled  water 
and  15  cc.  of  concentrated  sulphuric  acid.  Dilute  to  200  cc.  and 
titrate  with  the  permanganate  solution  until  a  pink  color  appears. 
Ten  cc.  of  the  permanganate  solution  should  be  required.  If  less 
is  required,  dilute  the  solution  slightly  and  repeat  the  test  until 
the  correct  strength  is  obtained. 

b.  Total  Sulphate  (as  SOS).    Weigh  out  1.0  gram  and  dissolve 
in  100  cc.   distilled  water.     Add  a  few  drops  of  concentrated 
hydrochloric  acid  and  about  8  cc.  of  ammonium  chlorid  (about 
1  to  4) .     Heat  to  boiling  and  add  a  slight  excess  of  barium  chlorid 


APPENDIX  245 

(10  per  cent),  to  precipitate  the  sulphate  as  barium  sulphate. 
Keep  near  boiling  point  for  several  hours  until  all  the  precipitate 
has  settled  out.  Cool  and  decant  the  clear  liquid  through  double 
filter  paper,  wash  the  precipitate  several  times  with  hot  water, 
pouring  the  wash  water  through  the  filter.  Finally  empty  the 
precipitate  on  the  filter  paper  and  wash  several  times  with  hot 
water.  Dry  the  precipitate  and  filter  paper  in  a  crucible  over  a 
Bunsen  flame  and  finally  ignite,  keeping  crucible  at  dull  redness 
for  10  minutes.  Cool  and  weigh.  The  weight  in  grams  multi- 
plied by  34.2  gives  the  per  cent  S03. 

Bleaching  Powder  (Penot  Method).  Weigh  out  7.17  grams 
and  place  in  a  mortar.  Add  a  little  water  and  rub  the  mixture  into 
a  smooth  cream,  add  more  water,  stir  and  allow  to  settle;  pour  the 
solution  into  a  liter  flask.  Mix  the  remaining  sediment  with  more 
water,  pour  into  flask  and  repeat  until  every  particle  of  powder  has 
been  transferred  from  the  mortar  to  the  flask.  Fill  the  flask  with 
distilled  water  to  the  liter  mark,  shake  thoroughly,  and  draw  off 
50  cc.  of  the  liquid  into  a  beaker.  Titrate  with  ^  alkaline  arsenite 
solution,  until  a  drop  of  the  mixture  taken  out  with  a  glass  rod 
gives  no  blue  color  with  prepared  starch  paper.  The  number  of 
cc.  of  arsenious  solution  used  gives  the  percentage  of  available 
chlorine. 


APPENDIX  B 

STANDARD  SOLUTIONS 

Distilled  Water.  The  purity  of  distilled  water  for  use  in  the 
preparation  of  standard  solutions  may  be  verified  by  the  following 
tests: 

a.  Ammonia  or  Ammonium  Compounds.     Add  10  drops  of 
Nessler  solution  to  50  cc.  of  the  water.     No  change  of  color  indi- 
cates freedom  from  ammonia  or  ammonium  compounds. 

b.  Chlorids.     No  change  in  color  or  precipitate  on  adding  a  few 
drops  of  nitric  acid  followed  by  silver-nitrate  solution  to  a  50  cc. 
sample  indicates  absence  of  chlorids. 

c.  Sulphates.     Add  J4  cc-  of  hydrochloric  acid  and  a  small 
amount  of  barium  chlorid  to  100  cc.  of  the  water.     If  no  pre- 
cipitate appears  in  12  hours,  sulphates  are  absent. 

d.  Nitrates.     Pour  5  cc.  of  diphenylamine  solution  into  a  test 
tube  and  add  10  cc.  of  the  water.     If  no  blue  color  appears  at 
contact  surfaces,  nitrates  are  absent. 

e.  Residue  on  Evaporation.     There  should  be  no  residue  on 
evaporating  100  cc.  of  the  water  to  dry  ness  on  a  water  bath. 

/.  Heavy  Metals  and  Calcium.  There  should  be  no  change 
on  treating  100  cc.  with  hydrogen  sulphid  water,  ammonia  water, 
ammonium  sulphid  or  ammonium  oxalate  solution. 

g.  Organic  or  Oxidizable  Matter.  Heat  100  cc.  of  the  water  to 
which  1  cc.  of  strong  sulphuric  acid  has  been  added  to  boiling. 
Add  a  drop  of  potassium  permanganate  and  boil  three  minutes. 
The  pink  color  should  persist. 

h.  Neutrality.  Water  should  be  pink  to  a  drop  of  erythrosin, 
but  color  should  be  discharged  by  a  drop  of  sulphuric  acid. 

Sodium  Carbonate,  Tenth  Normal  Solution.  Heat  10  grams  of 
chemically  pure  sodium  bicarbonate  in  a  weighed  porcelain  dish 
over  a  Bunsen  burner  for  about  thirty  minutes,  stirring  it  with  a 
platinum  wire.  The  dish  should  be  heated  to  a  dull  red,  care  being 
taken  not  to  fuse  the  bicarbonate.  Allow  the  dish  and  contents  to 
cool  in  a  desiccator.  (This  is  a  two-champered  glass  dish  with 
cover,  the  lower  compartment  containing  calcium  chlorid,  which 

246 


APPENDIX  247 

keeps  the  air  within  the  dish  absolutely  dry.  See  Fig.  95.)  When 
cool,  weigh  dish  and  contents.  Then  reheat  to  dull  redness,  cool 
in  desiccator  as  before,  and  reweigh.  If  there  has  been  any  loss  in 
weight,  reheat,  cool,  and  reweigh.  Continue  this  process  until 
weight  remains  constant.  When  cool,  weigh  out  exactly  5.3 
grams  on  an  accurate  balance  and  place  in  a  glass  vessel,  adding 
300  cc.  of  hot  (not  boiling)  water.  This  will  dissolve  the  sodium 
carbonate.  When  cool  pour  into  a  glass-stoppered  liter  graduate 
and  make  up  to  the  liter  mark  by  rinsings  of  the  glass  vessel  with 
distilled  water.  Insert  the  stopper,  shake  the  liter  graduate 
thoroughly,  and  transfer  the  contents  into  a  glass-stoppered  re- 
agent bottle.  Needless  to  say,  after  weighing  out  the  5.3  grams 
and  placing  them  in  the  glass  vessel  or  beaker,  no  stirring  rod  can 
be  introduced  to  aid  solution,  and  care  must  be  taken  that  not  a 
drop  is  spilled  in  transfer  to  the  graduate.  The  graduate  should  be 
filled  to  the  liter  mark  only  after  contents  have  cooled  to  the  tem- 
perature marked  on  the  graduate  (generally  about  room  tempera- 
ture.) In  transferring  the  normal  solution  to  the  reagent  bottle, 
the  latter  should  first  be  rinsed  out  with  some  of  the  solution. 

This  is  the  fundamental  standard  solution  from  which  the 
others  are  prepared.  As  it  does  not  keep  well,  an  f-0  sulphuric-acid 
solution  should  be  prepared  from  it  (see  below)  and  kept  as  a 
standard  against  which  to  check  the  other  acid  and  alkali  solutions 
from  time  to  time. 

Sodium  Carbonate  (f-0  =  one-fiftieth  normal).  Measure  out 
200  cc.  of  the  tenth  normal  solution  into  a  liter  graduate  with  a 
burette  and  make  up  to  one  liter  with  distilled  water.  Shake  well 
and  transfer  to  a  reagent  bottle,  using  the  customary  precautions. 

Sulphuric  Acid  (^  =  one-fiftieth  normal).  Pour  1  cc.  of  pure 
concentrated  sulphuric  acid  into  a  liter  of  distilled  water.  Insert 
stopper  in  graduate  and  shake  thoroughly.  Measure  out  50  cc.  of 
the  ^5  sodium  carbonate  with  a  pipette,  heat  to  boiling  and  titrate 
with  the  sulphuric-acid  solution,  using  methyl  orange  as  an 
indicator.  Dilute  and  retest  until  exactly  50  cc.  of  the  sulphuric- 
acid  solution  are  required.  Transfer  to  a  reagent  bottle,  using 
customary  precautions. 

Sulphuric  Acid  (f-0  =  one-twentieth  normal).  Pour  2  cc.  of 
pure  sulphuric  acid  into  a  liter  of  distilled  water.  Shake  thorough- 
ly. Measure  out  25  cc.  of  the  ^  sodium  carbonate  with  a  pipette 
and  titrate  at  boiling  with  the  sulphurrc-acid  solution,  with  methyl 


248  WATER    PURIFICATION    PLANTS 

orange  as  indicator.  Adjust  by  dilution  until  25  cc.  of  the  car- 
bonate are  neutralized  by  exactly  10  cc.  of  the  .sulphuric-acid 
solution. 

Hydrochloric  Acid,  Normal  Solution.  Weigh  out  181  grams 
of  20.2  per  cent  chemically  pure  hydrochloric  acid  (specific 
gravity  =  1.10),  and  pour  slowly  into  400  cc.  of  distilled  water. 
Allow  to  cool  and  transfer  to  a  liter  graduate.  Rinse  original  con- 
taining vessel  repeatedly  with  distilled  water,  pouring  rinsings 
into  graduate.  Make  up  to  liter  graduation  with  distilled  water, 
stopper  and  shake  well.  This  gives  an  approximately  normal 
solution.  For  greater  accuracy  titrate  with  normal  sodium  car- 
bonate, using  methyl  orange  as  indicator,  and  adjust  acid  solution 
until  equal  amounts  neutralize  each  other. 

Hydrochloric  Acid  (~  =  one-twentieth  normal).  Measure 
out  50  cc.  of  the  normal  acid  solution  into  a  liter  graduate  con- 
taining several  hundred  cc.  of  water  with  a  burette  and  make  up 
to  the  liter  mark  with  distilled  water.  Stopper  and  shake  thor- 
oughly and  transfer  to  a  reagent  bottle  in  the  usual  manner. 

Hydrochloric  Acid  (1:1  solution).  Pour  a  measured  quan- 
tity of  the  chemically  pure  hydrochloric  acid,  very  slowly,  into  an 
equal  amount  of  distilled  water.  Use  extreme  caution  to  prevent 
spattering  of  the  acid  or  overheating  the  water. 

Sodium  Hydroxid,  Normal  Solution.  Dissolve  50  grams  of 
chemically  pure  caustic  soda  (NaOH)  in  a  liter  of  boiled  distilled 
water,  after  first  washing  the  sticks  of  soda  in  CC>2  free  water, 
to  remove  carbonates  from  surface.  Shake  well  and  titrate  25  cc. 
with  normal  hydrochloric  acid,  using  methyl  orange  as  an  indica- 
tor. Adjust  by  dilution  until  equal  quantities  of  each  solution 
neutralize. 

Sodium  Hydroxid  (^  =  one-twentieth  normal).  Measure 
out  50  cc.  of  the  normal  solution  into  a  liter  graduate  and  make  up 
to  one  liter  with  distilled  water.  Stopper  graduate,  shake  well,  and 
transfer  to  reagent  bottle. 

Phenolphthalein  (Indicator).  Dissolve  1  gram  of  the  powder 
in  200  cc.  of  50  per  cent  alcohol. 

Erythrosin  (Indicator).  Dissolve  ^  gram  of  the  sodium  salt 
in  one  liter  of  distilled  water. 

Methyl  Orange  (Indicator).  Dissolve  1  gram  of  the  powder  in 
one  liter  of  distilled  water.  This  indicator  reacts  red  with  acids 
and  yellow  with  alkaline  solutions. 


APPENDIX  249 

Potassium  Permanganate  Solution.  Dissolve  5  grains  of 
the  pure  crystals  in  a  liter  of  distilled  water. 

Potassium  Sulphocyanid  Solution.  Dissolve  20  grams  of  the 
pure  salt  in  a  stoppered  liter  graduate  with  distilled  water  to  the 
liter  mark.  Shake  thoroughly. 

Soda  Reagent.  Using  the  normal  solutions  of  sodium  hy- 
droxid  and  sodium  carbonate  described  above,  measure  out  50  cc. 
of  each  solution  into  a  liter  graduate  and  fill  to  the  liter  mark  with 
distilled  water. 

lodin  Solution  (-^  =  one-tenth  normal).  Dissolve  12.7  grams 
of  chemically  pure  iodin  and  18  grams  of  chemically  pure 
potassium  iodid  in  about  25  cubic  centimeters  of  cold  distilled 
water,  transfer  to  a  liter  graduate,  rinsing  dissolving  vessel  into 
same  repeatedly,  and  make  up  to  one  liter  with  distilled  water. 
Shake  well  and  transfer  to  a  dark-colored  reagent  bottle.  Keep 
in  a  dark,  cool,  place. 

Alkaline  Arsenite  Solution  (~  =  one-tenth  normal).  Dis- 
solve 4.95  grams  of  the  purest  sublimed  arsenious  oxid  reduced 
to  powder  in  about  250  cc.  of  distilled  water  in  a  flask,  and  add 
about  20  grams  of  pure  sodium  carbonate.  The  mixture  needs 
warming  and  shaking  for  some  time  in  order  to  dissolve  com- 
pletely; when  this  is  accomplished,  it  is  diluted,  cooled,  and  trans- 
ferred to  a  liter  graduate.  The  flask  is  rinsed  several  times  into 
the  graduate,  and  the  solution  is  made  up  to  the  liter  mark. 

Test  the  solution  by  putting  20  cc.  into  a  beaker  with  a  little 
starch  solution  and  titrate  with  the  iodin  solution,  using  a  burette, 
until  the  blue  color  appears.  Exactly  20  cc.  of  iodin  solution 
should  be  required. 

Starch  Solution  (Indicator).  Mix  one  part  of  clean  potato 
starch  with  cold  water  into  an  emulsion,  gradually  pour  in  from 
150  to  200  times  its  weight  of  boiling  water,  and  boil  several 
minutes.  Allow  the  solution  to  settle  and  use  only  the  clear  por- 
tion, a  few  drops  sufficing  for  each  test.  The  solution  may  be 
preserved  by  adding  a  few  drops  of  chloroform  and  keeping  it  in  a 
stoppered  bottle. 

Starch  Paper  (Indicator).  Mix  a  small  amount  of  the  starch 
solution  with  a  few  drops  of  potassium  iodid  solution  on  a  dish  and 
soak  strips  of  pure  filter  paper  therein.  Use  while  still  damp,  as  it 
is  then  most  sensitive. 


250  WATER    PURIFICATION    PLANTS 

Nessler  Solution.*  Dissolve  50  grams  potassium  iodid  in  a 
minimum  quantity  of  cold  water.  Add  a  saturated  solution  of 
mercuric  chlorid  until  a  slight  but  permanent  precipitate  persists. 
Add  400  cc.  of  50  per  cent  solution  of  potassium  hydrate,  made 
by  dissolving  the  potassium  hydrate  and  allowing  it  to  clarify  by 
sedimentation  before  using.  Dilute  to  one  liter,  allow  to  settle 
and  decant. 

*  "  Standard  Methods  of  Water  Analysis,"  Am.  Pub.  H.  Assoc. 


APPENDIX  C 

SPECIFICATIONS   FOR   LIME,  SODA   ASH,   AND 

ALUMINUM    SULPHATE.      USED    BY    THE 

WATER  DEPARTMENT,  COLUMBUS,  O.* 

Lime.  All  lime  furnished  under  this  contract  shall  be  the  best 
quality  of  fresh-burned,  fat  lime,  crushed  or  ground  so  that  no 
lumps  shall  be  greater  than  2  inches  in  any  dimension. 

The  lime  shall  be  delivered  in  tight  box  cars,  loaded  in  bulk; 
especial  care  shall  be  exercised  to  close  all  openings  by  which  lime 
might  sift  out,  and  to  prevent  the  circulation  of  air  and  the 
admission  of  moisture. 

The  lime  shall  be  delivered  at  a  uniform  rate  of  not  less  than 
40  tons  per  week,  or  at  such  increased  rate,  not  to  exceed  125  tons 
per  week,  as  shall  be  directed. 

The  percentage  of  water  soluble  calcium  oxid  in  each  car-load 
lot  of  lime  delivered  will  be  determined  from  the  analysis  of  a 
composite  sample  collected  on  its  arrival  at  the  water-purification 
works. 

For  any  car-load  lot  containing  88  per  cent  of  water  soluble 
calcium  oxid  the  city  will  pay  to  the  contractor  the  price  per  ton 
stated  in  the  proposal. 

It  is  hereby  agreed  that  the  city  shall  pay  a  bonus  of  1J/2  per 
cent  of  the  contract  price  per  ton  for  each  1  per  cent  by  which  the 
water  soluble  calcium  oxid  in  any  car-load  lot  delivered  shall 
exceed  88  per  cent,  and  shall  deduct  a  penalty  of  1  Yi  per  cent  of 
the  contract  price  per  ton  for  each  1  per  cent  by  which  the  water 
soluble  calcium  oxid  in  any  car-load  lot  shall  be  less  than  88  per 
cent. 

If,  in  any  car-load  lot,  the  material  as  delivered  shall  contain 
less  than  82  per  cent  of  water  soluble  unslacked  calcium  oxid,  it 
will  be  rejected  and  shall  be  removed  by  the  contractor  at  his  own 
expense,  and  the  cost  of  unloading  the  material  from  and  reloading 
into  the  car  shall  be  deducted  from  the  amount  payable  to  the 
contractor  under  the  terms  of  this  contract. 

*  Courtesy  of  Mr.  Charles  P.  Hoover,  chemist  in  charge. 
251 


252  WATER    PURIFICATION    PLANTS 

The  car-load  lot  as  a  unit  will  be  used  as  the  basis  of  accounting 
for  determining  the  amount  payable  to  the  contractor. 

Soda  Ash.  The  soda  ash  shall  be  that  known  as  58  per  cent 
light  soda  ash  and  shall  contain  not  less  than  98  per  cent  of  pure 
sodium  carbonate.  The  material  shall  be  in  dry,  powdered  form, 
shall  contain  no  large  lumps  or  large  crystals,  shall  be  free  from 
chips  and  other  foreign  matter,  and  not  more  than  0.5  per  cent 
shall  be  insoluble  in  cold  distilled  water. 

The  material  shall  be  delivered  at  a  uniform  rate  of  not  less  than 
20  tons  per  week,  or  at  such  increased  rate,  not  exceeding  90  tons 
per  week,  as  shall  be  directed. 

The  soda  ash  shall  be  packed  in  duck  sacks  to  be  furnished  by 
the  city,  but  the  contractor  shall  furnish  the  twine.  Each  sack 
shall  contain  not  less  than  98  nor  more  than  102  pounds  of  the 
material. 

The  contractor  shall  handle  the  bags  with  care,  and  for  each 
sack  which  is  delivered  to  him  in  good  condition,  and  which  is 
damaged,  other  than  by  ordinary  wear  and  tear,  or  which  is  lost 
and  not  returned  to  the  city,  the  contractor  shall  pay  the  sum  of 
20  cents,  the  same  to  be  deducted  from  the  amounts  payable  to 
him  under  this  contract.  Any  bags  received  by  the  contractor  in  a 
condition  unsuitable  for  refilling  shall  be  set  aside  and  returned  to 
the  city.  The  material  shall  not  be  packed  when  in  condition  to 
damage  the  sacks. 

Each  car-load  lot  of  material  will  be  analyzed  on  delivery,  and 
the  acceptance  of  the  lot  will  be  determined  by  the  amount  of  pure 
sodium  carbonate  and  of  insoluble  matter  shown  by  this  analysis 
to  be  present. 

If  the  material  in  any  lot  shall  contain  less  than  98  per  cent  of 
pure  sodium  carbonate,  or  more  than  0.5  per  cent  of  insoluble 
matter,  it  will  be  rejected,  and  shall  be  removed  by  the  contractor 
at  his  own  expense,  and  the  cost  of  unloading  and  reloading  the 
material  shall  be  deducted  from  the  amounts  payable  to  the  con- 
tractor on  this  contract. 

The  car-load  lot  as  a  unit  shall  be  the  basis  of  accounting  for 
determining  the  amounts  payable  to  the  contractor. 

Sulphate  of  Alumina.  The  material  shall  be  that  known  as 
basic  sulphate  of  alumina,  containing  no  free  acid.  It  shall  be 
crushed  into  small  lumps  ranging  in  size  from  0.5  inch  to  2J/2 
inches,  and  shall  be  free  from  chips  and  other  foreign  matter.  It 


APPENDIX 


253 


shall  contain  not  less  than  17  per  cent  of  available  water  soluble 
alumina,  A^Os,  and  of  this  alumina  content  there  shall  be  at  least 
3  per  cent  of  its  weight  in  excess  of  the  amount  theoretically  re- 
quired to  combine  with  the  sulphuric  acid  present.  The  material 
shall  contain  not  more  than  0.5  per  cent  of  matter  insoluble  in 
cold  distilled  water. 

Sulphate  of  alumina  shall  be  shipped,  unsacked,  in  tight  box 
cars;  the  cars  shall  be  thoroughly  cleaned  before  loading,  the  door 
openings  shall  be  boarded  up  to  a  suitable  height,  and  all  openings 
by  which  the  material  might  waste  shall  be  carefully  closed. 

Each  car-load  lot  of  material  will  be  analyzed,  on  delivery,  and 
the  acceptance  of  the  lot  will  be  determined  by  the  amount  of 
alumina  and  of  insoluble  matter  shown  by  this  analysis  to  be 
present. 

If  the  material  in  any  car-load  lot  as  delivered  fails  to  meet  these 
specifications  it  will  be  rejected  and  shall  be  removed  by  the  con- 
tractor at  his  own  expense,  and  the  cost  of  unloading  and  reloading 
the  material  shall  be  deducted  from  the  amounts  payable  to  the 
contractor  under  this  contract. 

The  car-load  lot  as  a  unit  shall  be  the  basis  of  accounting  for 
determining  the  amounts  payable  to  the  contractor. 

APPENDIX  D 

WEIR  TABLE 
GIVING  FLOW  IN  GALLONS  PER  MINUTE  OVER  A  WEIR  12  INCHES  WIDE 


Depth, 
in  Inches 

Gallons, 
per  Minute 

Depth, 
in  Inches 

Gallons, 
per  Minute 

Depth, 
in  Inches 

Gallons, 
per  Minute 

1 

36 

4% 

375 

8^ 

900 

11A 

50 

5 

405 

8% 

939 

1% 

66 

&A 

436 

9 

979 

IK 

84 

5y2 

468 

9% 

,020 

2 

102 

5% 

500 

$1A 

,062 

2% 

122 

6 

533 

9% 

,104 

VA 

143 

6% 

567 

10 

,147 

2% 

165 

6^ 

601 

10M 

,190 

3 

188 

6% 

636 

10^ 

,234 

3^ 

212 

7 

672 

10% 

,279 

3^ 

237 

7% 

708 

11 

,323 

3% 

263 

ly*. 

745 

11M 

,369 

290 

7% 

783 

HH 

,414 

4% 

317 

8 

821 

11% 

,461 

4H 

346 

8M 

860 

12 

,508 

INDEX 


Acidity,  interpreting  test  for,  136 
Adsorption,  defined,  10 
Agar,  preparation  of,  124 
Alarms,  electric,  214 
Algae,  defined,  13 
Alkalimetry,  109 
Alkalinity,  test  for,  104 

interpreting  test  for,  135 

limiting  values,  135 
Alum,  free,  how  remedied,  139 

test  for  free,  115 
Aluminum  sulphate,  described,  144 

analysis  of,  243 

as  a  coagulant,  145 

determining    amount    required, 
examples,  147 

specifications  for,  252 
Ammonia,  free,  12 

albuminoid,  12 
Apparatus,  preparing,  123 
Arnold  sterilizer,  119 
Arsenite  solution,  preparation  of,  249 
Autoclave,  119 
Automatic  recorders,  213 
Automatic  regulation  of  coagulants, 
176 

Bacteria,  description,  13 

diseases  caused  by,  13 

in  sewage,  13 

interpreting  tests,  140 

standard,  141 
Bacterial  tests,  117 
Baffles,  190,  191 
Basins,  cleaning,  192 
Bicarbonates,     determination     from 

test,  111 

Bile,  lactose,  preparation  of,  126 
Bleach,  165 
Bleaching  powder,  analysis  of,  245 


Brass,  corrosion  of,  11 

Bronze,  corrosion  of,  11 

Broth,  dextrose,  preparation  of,  126 

Burrette,  99 

Calibration  of  apparatus,  204 
Carbonates,  determination  from  test, 

111 
Carbonic  acid,  test  for,  106 

corrosive  effect,  137 

in  acid  water,  107,  109 

interpreting  test  for,  136 

in  water,  8 
Casserole,  100 
Centimeter,  97,  98 
Charts,  drawing  of,  214 
Chester,  J.  N.,  74 
Chlorine,  available,  165 

liquid,  170 
Clark,  Wm.  G.,  92 

Cleaning  basins,  when  necessary,  192 
Clear-water  basin,  46,  204 
Coagulant,  preparing  solutions  of,  194 
Coagulants,  analysis  of,  243 
Coagulating  apparatus,  34 

basins,  65 
Coagulation,  defined,  21 

natural,  162 

process,  142 

theory,  143 

Coli,  significance  of,  141 
Collectors,  filtered  water,  40 
Colloidal  solution,  defined,  5 
Color,  apparent,  10 

interpreting  test  for,  133 

in  water,  10 

standards,  103 

test  for,  103 

Columbus,  softening  plant  at,  74 
Controllers,  rate  of  filtration,  44 


255 


256 


INDEX 


Conveyor,  for  lime  at  Columbus,  83 
Copper  sulphate,  174 
Costs  of  coagulation,  164 

of  filtration,  208 
Crenothrix,  7 
Currents,  in  basins,  190 

Desiccator,  243 
Diffusion,  8 
Distilled  water,  94 

test  for  purity  of,  246 

Economy  of  operation,  217 
Effective  size  of.  sand,  defined,  23 
Ejector,  for  sand,  28 
Erythrosin,  105 

preparation  of,  248 

Felspar,  action  of  water  on,  5 

defined,  4 
Fermentation,  of  dextrose  broth,  130 

of  lactose  bile,  131 

tubes,  128 

Ferrous  bicarbonate,  7 
Ferrous  sulphate,  analysis  of,  244 

as  a  coagulant,  157 

corrosive  effect,  138 

described,  156 

examples  of  use,  159 

free,  how  remedied,  140 

test  for  free,  115 
Filter,  device  for  media,  124 
Filters,  details  of  Washington,  52,  53 

operation  of,  198 

washing,  201 
Filtration,  mechanical,  31 

slow  sand,  22 

theory  of,  26 
Fuller,  George  W.,  90 
Fungi,  defined,  13 

Gages,  required  for  each  filter,  47 
Gallates,  cause  of  color,  10 
Gelatin,  preparation  of,  123 
Graduate,  98 

Hardness,  permanent,  acquisition  of,  6 
Hardness,  temporary,  acquisition  of,  6 
Hazen,  Allen,  23 


Head  house,  at  Minneapolis,  66,  67 
Hematite,  7 
Hering,  Rudolph,  90 
Hoover,  Charles  P.,  90 
Hydrochloric  acid,  standard  solutions 

of,  248 
Hydroxids,  determination  from  test, 

111 
Hypochlorite  of  lime,  165 

analysis  of,  245 

dissolving  device,  39 

dissolving  device  at  Minneapolis, 
69 

preparation  of,  167 

test  for  excess,  116 
Hypochlorite,  sodium,  171 

Ice  box,  120 

Incrustants,  test  for,  185 
Incubator,  120 
Indicators,  action  of,  109 
Inspection  of  filter  plant,  197 
Introduction  of  chemicals,  163 
lodin  solution,  preparation  of,  249 
Iowa  City,  iron  removal  plant,  90 
Iron,  distribution  in  nature,  7 

interpreting  test  for,  137 

removal,  51 

sugar  of,  156 

test  for,  113 

Laboratory,  requirements,  47 

management  of,  204 
Lime,  analysis  of,  243 

described,  150 

dry  feeding  of,  153 

hydrated,  152 

slaking,  151,  194 

specifications  for,  241 
Liter,  97,  98 
Litmus  solution,  127 
Logwood  test  for  alum,  115 
Loss-of-head  in  slow  sand   filtration, 
24 

Magnesium,  test  for,  184 
Measuring  bottle,  98 
Mechanical  filtration,  31 


INDEX 


257 


Media  for  bacterial  tests,  123 

notes  on,  127 
Meter,  97,  98 

Venturi,  45,  76 

Methane,  presence  in  water,  9 
Methyl  orange,  preparation  of,  248 
Metric  system,  97,  98 
Millimeter,  97,  98 
Mine  drainage,  11 
Minneapolis,  filters  at,  62 
Mixing  tanks  at  Columbus,  76 

Negative  head,  33 

Nessler  solution,  preparation  of,  250 
Nitrates,  presence  in  water,  7 
Nitrogen,  presence  in  water,  9 

Odor,  designation,  100 

test  for,  100 
Organization,  206 

diagram,  207 
Orifice  box,  constant  feed,  178 

described,  36 

at  Iowa  City,  91 
Oxygen  in  water,  8 

solubility  of,  9 
Ozone,  176 

Paper  mill  waste,  12 

Permanganate   solution,   preparation 
of,  239 

Phenolphthalein,  106,  248 
preparation  of,  248 

Pipette,  98 

Plates,  221-241 

Plating,  in  bacterial  test,  128 

Potassium     permanganate    solution/ 
preparation  of,  249 

Potassium     sulphocyanid,    prepara- 
tion of,  249 

Precipitation,  source   of   water   sup- 
ply, 3 

Primary  waters  defined,  5 

Protozoa,  15 

Raking  slow-sand  filters,  28 
Rate  controllers,  adjustment  of,  199 
Rate  of  filtration,  rapid  sand,  31 
slow  sand,  25 


Records,  211 

automatic,  213 

Regulator  houses  at  Washington,  53 
Runoff,  defined,  3 

Salt,  least  amount  detected,  12 

pollution  by,  12 

Samples,  collecting  bacterial,  127 
Sand  bins  at  Washington,  55 
Scale,  automatic,  at  Columbus,  85 
Schmutzdecke,  26 
Scioto  River,  75 
Scraping  slow-sand  filters,  28 
Secondary  waters,  defined,  5 
Sedimentation,  189 
Settling  basins,  33 
Settling  basins  at  Columbus,  79 
Sewage,  source  of  pollution,  12 
Slaking  device  at  Minneapolis,  68 
Soda  ash,  analysis  of,  243 

described,  154 

examples,  155 

specifications  for,  252 

uses  of,  154 

Soda  reagent,  preparation  of,  249 
Sodium  carbonate,  standard  solutions 

of,  246 
Sodium   hydroxid,    normal   solution, 

248 
Sodium      hypochlorite,      electrolytic 

preparation  of,  171 
Sodium  thiosulphate,  169 
Softening  water,  180 

examples,  186 

reactions  of,  183 

special  tests,  184 
Solutions,  standard,  246 
Specifications  for  chemicals,  251 
Sponges,  fresh-water,  15 
Starch  paper,  preparation  of,  249 
Starch  solution,  preparation  of,  249 
Statistics,  211 
Sterilization,  164 

in  slow-sand  filtration,  30 
Sterilizer,  dry,  117,  118 

Steam,  119 
Still,  94,  95 
Storage  bin,  for  lime,  Columbus,  85 


258 


INDEX 


Strainers  in  collector  pipes,  41,  43,  81 
Sugar  of  iron,  156 

analysis  of,  244 

Sulphuric    acid,    standard    solutions 
of,  247 

Table,  operating,  for  filters,  50 
Tank,  for  air  and  water,  75 
Tannates,  cause  of  color,  10 
Tannery  waste,  12 
Taste,  interpreting  test  for,  132 

test  for,  100 
Telephones,  214 
Tests,  frequency  of,  193 

list  of  essential,  93 
Thallophytes,  defined,  13 
Torresdale,  filters  at,  58 
Turbidity,  test  for,  100 

bottle  standards,  102 

coefficient,  133 

interpreting  test  for,  133 

measurement  of,  4 

reciprocal,  101 


Turbidity,  rod  for  measuring,  101 

table  of,  101 

Typhoid,  reduction  in,  due  to  filtra- 
tion, 19 

Ultra-violet  rays,  174 
Uniformity   coefficient   of    sand   de- 
fined, 23 

Valves,  controlling  filters,  47 
Venturi  meter,  45,  76 

Wash  bottle,  94 
Washer  for  sand,  28,  54 
Washing  filters,  201 
Washing,  rapid  sand  filters,  46 
Washington,  filtration  plant,  51 
Water,  constituents  of,  1,  2 

distilled,  94 

softening,  51,  180 

typical,  analyzed,  15 
Weir  table,  253 
Wilkinsburg,  filter  plant  at,  71 


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